I'm thinking minor this is a pretty narrow focus, IMO. I reserve the right to restrict things that are "too powerful" but I don't know what that is now. 
Let's start Mysteries sometime after we get underway.
Why Ex Misc is simple. I need the extra virtue 
I did the write-up from some very crumbled notes and the old back-story was fitted very closely to Irencilla, but also very saga specific and not too close to the 5th ed Faeries and Merinita. So it probably need a rewrite and refinement.
I agree that the aging focus doesn't fit too well with the healer part, so I'll rewrite that when I expand it a bit. The Puissant or maybe even better the affinity with Creo would fit better and then the tradition flaw would be the Perdo deficiency. Healers don't do Perdo, and Creo is the healer's tool. It would also fit well being able to heal not only Corpus but also Herbam and Animal.
On the subject of being swallowed by Merinita I have an idea that the tradition could actually be a political paw or player between (the few political) Ex Misc and Merinita. The tradition is not supposed to be about the fay, but about fay based in stories about healing people, crops and animals. The classical "helpful stranger in the cottage in the wood" story, which sometimes is a faerie and sometimes a part of the Faerie Healers tradition (and sometimes some other hedge witch or simply a herbalist or con-man 
)
I'll try rewriting later when I'm not so tired as on Sunday. Thanks for the comments.
And the haughty attitude from "stuck in the past" traditionalists is as it should be
Just a quick note that I am going to advance Petronius a few years (5-10) to represent time spent as a peregrinatores before the founding of the covenant. It is during this period that he will have gathered resources for the new covenant.
I plan on doing this season-by-season. Should I still go with (on average) the 30 points per year as described in the core book (page 32)? From some experiments advancing characters before, this seems mostly fair, except that it is harsh on learning new spells because it does seem to take into account lab text availability. That's an important point for Petronius because as a Mercurian formulaic spells are essential if he wants to do magic quickly (he casts all spontaneous magic via Ceremonial Casting, so 15 minutes/magnitude).
It makes accounting easy. Our beginning spell repitoires will be smaller, but our Arts scores will be a big greater. I did this in Bibracte for two reasons, the accounting I already mentioned, and 2, to represent being held back in their previous environments.
In this saga/simulation I think it models the pursuit of a new covenant goal pretty well. It makes sense that we might spend less time learning spells and more time out improving Arts and Abilities while hunting for vis sources and a covenant spot.
Oh, and Mercurian Magic generally drives me nuts, the disadvantage of that major flaw outweighs most of the advantage, and I've house ruled it in Bibracte so that Mercurians can cast spontaneously as normal, but receive a +5 bonus above and beyond Artes Liberales and Philosophae for ceremonial casting. They also cast all Ritual spells as if they had Stalwart mastery on them, without spending experience points (or receiving reduction in botch dice) for the mastery ability. I'm not averse to doing that here, since I think I'll HR it that way in all sagas I run going forward.
Actually, I wanted to try Mercurian Magic as is to see just how limiting it is. I almost went with no spontaneous magic at all (by adding Weak Spontaneous Magic), but figured that would be too extreme and would make it almost impossible for the character to investigate magic on-site (as opposed to in the lab).
As for the Stalwart mastery, I don't really see it as having a huge effect. A more general HR could have been that all ritual spells automatically have 1 level of mastery when learned, leaving it to the magus to decide which one is more helpful for a specific spell. But that's not a request for this saga, just a comment on your proposed HR for all your sagas.
Certainly don't need to do it here, this is a bit of a different animal. As far as the Stalwart Mastery, it becomes an issue when a PC is casting more than one healing ritual because Harco was attacked and the Magical Mercere is trying to heal as many redcaps as he can. After 4 healing rituals he's about done, since a ritual automatically instills at least 1 level of long term fatigue. With Stalwart, he could catch his breath for a few minutes to recover. It's not going to happen often, but it could happen...
I hadn't thought of that. It certainly is a handy mastery for healing. On the other hand, it is fairly useless for something like the Aegis, where Adaptative Casting (or even Penetration) would be more appropriate. Conjuring the Mystic Tower, on the other hand, would probably benefit more from Precise Casting.
All I'm saying is that Stalwart Casting is not always the best choice, or even particularly useful. It might not suit the magus' style at all. Which is why I mentioned tht simply giving the Mercurian magus 1 level of mastery might be a better option.
On a totally different subject...
Since a familiar is very nice, how are we handling these questions:
- Finding a familiar. I think Hippocrates would like to find a familiar very early, probably during the "30 XP per year" period. Is spending a season and then finding one an acceptable way of doing it?
- Familiar progression. How do we progress familiars? I am used to letting a familiar progress as a non-magical animal (that is without any penalties, like any character) since that gives a fairly good reason for an immortal (a magical beast) to give up immortality (to gain the possibility of improvement).
- Familiar powers. Do the magus/player design it themselves according to RoP:Magic? (And then put it to the troupe for approval)
- Focus and familiars. How will a focus interact. Since you're supposed to be able to find a familiar matching your chosen (best) arts without much trouble, should you also be able to find one where your focus applies?
And on the subject of best arts, any suggestions for a Creo Corpus familiar (sort of) available in Rhine? Traditionally a small serpent could fit. It is connected to Medicine through Greek traditions (rod of Asclepius being entwined by an aesculapian snakes)
Fine with me.
These days they just start aging once again (which might mean anything for a magical animal, mind you.
Also, I'm fine with simple progression, though I'd probably not give familiars Exposure XPs - just to keep book keeping down.
Debate might be a better word than approval, but fine with me
Serpents are fine in the Rhine - half the mythological fauna of the area appears to be serpentine.
Even Denmark (and Sweden) has Vipers (or is it adders, never kan remember) - I recall nearly stepping on one.
I think that JL will have the final word on this, but here's my oppinion.
Seems fine to me. Unless you want to introduce some kind of "luck" into the equation. After all, you never know how long you may have to look... Maybe something like 30% chance of finding one every month you look for one. This is not necessarily exclusive of getting experience during that season, since this is basically a story. So xp related to the search can defenitively be appropriate, whether theorical (Magic Lore, Area Lore) or practical (Stealth, Hunting, Athletics, and many others).
I would be really wary of abuse there. I've seen too many familiars optimized as lab assistants. It is sooo tempting to stack study in MT, powers that can help lab work, etc. At best, I would suggest that a familiar can gain only 1/3 of the xp a regular character would.
I've tried using the rules from RoP:M and they are a bit of a headache due to complexity. Troupe (or at least SG) approval is certainly a must. You might want to go with a process similar to magus creation -- present a concept, take suggestions, build the stats, have the stats adjusted by the troupe.
Not sure it should apply. Depends on the focus. A focus in Aging is though to apply to a familiar (and so is a focus on Portals, BTW). I think the focus should only apply if it is very closely related to the familiar in question, or to familiars in general. So a focus in snakes would apply to a serpent familiar.
There's the serpent suggested by Tellus. Homonculus-type magical creature? Maybe a magical imp?
RoP:M suggest the following for Corpus-related familiars: caladrius, cat, dog, goose, mandrake. For Creo,it suggests: beaver, eagle, lizard, pelican, weasel, any animal that can rejuvenate itself.
So maybe a small lizard with a minor human-healing power?
I like the mandrake, really.
And the viper, obviously 
I'm not against getting a familiar now, but it does make it a bit complicated.
First issue is you need a season to find and a season to bind. In play, there's a season of adventure with XP and finding the familiar, followed by the binding. In character generation, you lose 10 xp for the season to find it. Then there's the season to bind it, and again you lose another 10 xp. And there's no exposure during character generation, because it is too much of a headache to track. So you have two seasons of that year left, and you only get 10 xp (30 xp per year, per RAw on page 32 of the MRB). You might as well lose the 10 xp and take the rest of that year to enchant something: a season to prepare for enchantment and a season to invest. It's probably best to do this at the tail end of your advancement, so you can keep track of stats more easily.
I'd say the focus would not apply, but something creative might make me change my mind.
RoP:Magic, sure if you want to do all that work, it also means a bit more work for the troupe, I'd rather it happen in play if you want to do this then. At the start of things there are a lot of moving pieces and it is easy to miss something. It helps if you have MetaCreator. And, of course, don't abuse it. 
I'm generally against the whole must consume vis to learn thing.
The things about Arthur and stories would apply during play but should not apply during character generation.
I've been thinking about this some more. Instead of the Stalward mastery and the ceremonial casting requirements, what if we allowed Mercurians to commune and retain the vis savings?
This Major Hermetic has so many negatives to it, unlike every other Major Hermetic virtue that it needs something to differentiate it. Especially in a world where Wards and Aegis must penetrate. I've seen very few Mercurians and they've almost always been HR in some way.
Yep, that could certainly work. We could simply state that the vis-saving applies as long as the Mercurian is the one leading the ritual, even when non-Mercurian join in using WC. Also, the Mercurian must also know the ritual being cast, or he cannot lead (and so cannot apply his vis-saving to the ritual).
The draft stats for Rufus the Cat, Petronius' Magical Animal Companion. I've used the basic template of a cat and adjusted to a Summer animal. So I only added some virtues and flaws, xps, as well as magical power. Note that Rufus is a wild cat, much more feral than a cat living near humans. As such he's just beginning to get used to humans and is still observing them from a safe perch, learning what he can. The reason why Rufus befriended Petronius is because he felt kinship over the human (affinity with portals), which explains why Rufus' main power is so close to Petronius' area of interest. I've also given Rufus some good, though short-term, powers to increase his fighting abilities. This seemed to make sense for a feral cat.
Note that although Petronius will eventually make Rufus his familiar, but that for the moment Rufus has not yet accepted this. Communication is still fairly basic between the two, as Petronius' ability to understand Rufus is limited. If someone wants to play Rufus during the stories, that might be fun.
I'm open to suggestions and changes.
(Edit 2: Moved the stats here)
I debated about this one, and decided to try it out, but I don't know enough detail about the Church in the area to really know if being a priest and a magus would be possible. Somewhere along the line, I was imagining the "itinerant friar" model. I'll think about it more ... anyone else have thoughts on this?
I'll probably go with never actually taking Holy Orders, having been "rescued" by the visiting magus.
The following HR was mentioned on the general board, and I figured this might be a possibility for this saga. Seems like a good balance between unchecked familiar progression and the RoP:M rules that cripple familiar advancement.
It's one of the better ones I've seen. My problem with the whole "magical creatures don't learn and live forever" is that I have a serious problem seeing any kind of motivation for a magical animal to become a familiar with those rules in place. Taken at its most strict a familiar with anything but minuscule might would never learn anything without eating vis. And would gain close to nothing on a "upgrade" from Magical Animal Companion to Familiar. Actually it would lose out on immortality (since a familiar typically dies closely after it's master) and give up some freedom (the bond).
And with those rules combined with the possibility (I seem to remember from somewhere) of a mundane familiar, that suddenly becomes a mechanically much better choice. No might, no learning restrictions -> much higher skill for helping and discussions.
Well, I'll have to take a look again if I want to skip a year (that is "do Hippocrates have some lab-work he would like to do") before I decide.
If we want it really simple we just drop the role-playing and book keeping 100% and let the familiar learn as a grog at 15 XP per year. It reduces book-keeping and optimizing quite nicely while still keeping familiars advancing steadily.
I've advanced my magus to 6 years PG. See the advancement log and his current stats. Not that as part of the advancement, he now has an active longevity ritual created by his pater.
Here is a version of Aedituus at Gauntlet. I still need to determine spells, and having recently received HoH:MC, and quickly read the Criamon chapter, I am leaning toward Aedituus following the Path of Walking Backwards, possibly reaching the first station before arriving at the Covenant.
Aedituus ex Criamon
Characteristics: Int +2, Per +1, Pre 0, Com +2, Str 0, Sta +1, Dex 0, Qik -1
Size: 0
Age: 33
Decrepitude: 0 (0)
Warping Score: 0 (0)
Confidence Score: 1 (3)
Personality Traits: Patient +1, Impulsive +2
Virtues and Flaws: The Gift, Hermetic Magus, The Enigma, Affinity with Magic Theory, Book Learner, Educated, Gentle Gift, Puissant Mentem, Second Sight, Sense Holiness and Unholiness Student of the Divine; Deficient Rego, Noncombatant, Pious, Visions, Vow (of celibacy), Weird Magic
Abilities: Britain Lore (History) +1, Awareness (alertness) +2, Charm (first impressions) +1, Chirurgy (setting bones) +1, Concentration (reading) +3, Folk Ken (clergy) +2, Guile (lying to authority) +1, French (slang) +2, Church Lore (politics) +2, Profession: Scribe (neat work) +4, Teaching (Latin) +2, Artes Liberales (ceremonial magic) +3, Latin (Hermetic usage) +5, Medicine (physician) +1, Theology (heresy) +2, Code of Hermes (mundane relations) +1, Dominion Lore (saints) +2, Enigmatic Wisdom +1, Criamon Lore (personalities) +1, Magic Theory (Creo) +5, Parma Magica (Mentem) +1, Penetration (Mentem) +2, Second Sight (ghosts) +1, Sense Holiness/Unholiness (good) +2.
Arts: Cr 8, In 2, Mu 2, Pe 2, Re 2, An 0, Aq 0, Au 1, Co 7, He 3, Ig 0, Im 3, Me 7, Te 0, Vi 3
Character Concept: Abelard was the fifth son of a wealthy land owner in England. His mother died while giving birth to him, and his father donated a large sum of money, along with Abelard, to a local monastery, in exchange for prayers said for his beloved wife. Born with a birthmark on his left side, Abelard was always a strange child, and not always trusted by the monks, as he sometimes seemed to know what they were thinking. Most tolerated him however, and at the age of 18, Abelard was on the verge of taking Holy Orders. He had been hopign this would ease his sense of loneliness, even among the monks of the order, but his spirit still felt the need for something else as his ordination day approached. When a wandering scholar stopped at the monastery, he asked if Abelard might join his entourage, and provided the monastery with a generous donation in exchange for the young man. The Jerbiton magus recognized the Gift in the young monk, but not being in need or desire for an apprentice, paid off a debt to a Criamon maga with the gift of an apprentice. The maga was careful to try to preserve her apprentice's supernatural abilities upon opening his Arts, recognizing their value for a Criamon. She was never able to completely distract him from his monastic vows, and gifted him with the name Aedituus at his gauntlet. Aedituus continues to shave his head in a tonsure, and dresses in plain black robes, cinched with a white rope belt. He has been following the Winding Path since his gauntlet, and seeks to develop ideas about the relationship between the Enigma and the Divine.
EDIT: changed ability from Civil and Canon Law to Medicine, and swapped Au and He scores.