I’ll try my hand at SG for the toys. I’ll need to rough out a plan of what’s desirable. It’s been a long time since I SG’ed.
I'm sure you'll do fine. 
And you probably have until we recruit a new player or two to actually carry out the adventure.
Scott
That seems fair. What stats are we using? Is Fray going to donate/sell these to the covenant for its library?
Scott
He will be studying them to raise his arts from zero, and then much later use for an apprentice. Fray would be happy to loan them to the library for all to use.
Scores might be 5/15 in each, he's seeking starting books in all arts.
Which characters will be playing in the story for the toys? Just want to know what type of challenges to throw.
When we started the previous thread, Calliope got invited along - I'm happy to play or not play her as you'd prefer. (She's really meant to be an NPC, but...)
If you'd rather bring Gregorius or even a companion, do that. But it's up to you. 
Scott
Gregorius is going to leave the faerie regio to the specialists, now it's been found.
[To be honest, faerie stories don't massively excite me, especially if they're tending more towards the "fairies as weird things doing weird stuff" end of the spectrum, which the initial trip seemed to tend towards.]
If you don't want to play in that story, feel free to sit it out, though we might need someone on occasion to play the grogs.
Scott
Magus concepts:
- a Tremere fortifications maker - an existing character has requested one, so I could make one, turn up to make buildings and review the fortifications, and then stay around for a few years to read the library and see if there's any interesting buildings in the area
- a Flambeau who is an Aquam specialist, who throws corrosive liquids at the monsters he hunts and creates wine, beer and oil to sell for his covenant.
Companion concepts:
- a nomad with Premonitions who feels something important will happen with the covenant, and wants to help. Are the locals Kipchaks?
- a Byzantine merchant wanting to make use of the trade routes up the River Don.
New magi character concept
Flambau inducted in to the cult of Mercury straight after the end of apprenticeship. Flawless Magic from apprenticeship with Mercurian Magic/Pagan from joining the cult of Mercury. Wields fire and also has a number of healing rituals. He is a Dwarf, but make fun of the fact at your peril (Tyron Lannister is the image in my head). He would be two years out of apprenticeship.
Companion
Middle aged weapon master who cowardly fled the siege of Constantinople while most of his students died in defence of the walls. The remainder, many noble, are now enemies of him and any who harbour him.
Magus concepts:
- a Seeker ex Bonisagus, searches for magical sites, second sight, Intellego Vim, student of magic, definitely not a lab rat
- Stonemason, MuTe heavy, potentially Giant Blooded Verditius building enchanted structures.
Companion concepts: none yet
I think most of these could work to a greater or lesser extent. As far as buildings go, the covenant is in the ruins of a greek (/roman client) settlement (although so far nothing about the remaining buildings has struck us - we haven't really been looking, though), and there is a local necropolis which did have some tombs with odd features linked to architecture.
Note that there's a three year wait in the charter before a visitor can become a magus, and the saga has so far been fairly slow paced (so depending on your definition, it wouldn't become "his" covenant for a while).
The locals are Kipchaks, yes. There's a bit on them in this post: Covenant
I think the main trade goods down the Don are furs and slaves.
Be aware that Gregorius tends to be quite anti-paganism (he tends in general to very much believe the Tremere party line). That's not necessarily an OOC reason not to play a pagan, but you should be aware going in there's likely to be IC friction.
Well, we're remote enough for it to seem a good hiding place! We might want to focus of the animosity primarily on him, though - otherwise it becomes more of a covenant flaw than a character one.
Trogdor was playing a Seeker, but he hasn't posted since April (and there's no fundamental reason we can't have multiple Seekers). The covenant aura is variable and seems linked to water for some reason we haven't fully figured out yet (although strong links to Neptune/Poseidon probably figure in there somewhere), and as mentioned earlier there's a local necropolis with some interesting stuff in it.
For the Verditius, I think you need to figure out a hook for why he's out here - it doesn't not work, but it's not an obvious choice either.
Could be a great reason for the cult of Mercury wanting him to join the covenant in making sure their "world view" gets an airing. OOC I have no issue with the character conflict.
However, another option would be to take another year past apprenticeship and join the Neo Mecurians described in The Mysteries as they also initiate Mercurian Magic but it takes a year rather than a season and does not necessarily require the Pagan flaw.
Rereading the relevant sections of the books, the Cult of Mercury is a society rather than a Mystery Cult, and doesn't do initiations. If you want both Flawless and Mercurian Magic it would therefore need to be through the Neo-Mercurians.
The cult of Mercury ritual to obtain the Mercurian virtue is in the Provençal tribunal book Faith and Flame. It is the only mystery mentioned in what I agree is actually a society.
If you can let me know what you would consider a reasonable normal Pre plus Mystery Cult lore for a "normal" mystagogue would be for the campaign and I will design a set of initiation scripts for your initial review and comment.
Thanks
John
How do you treat Wizards Communion in the campaign. Mercurian Magic gives a free Wizards Communion at the highest ritual spell the magus has but it is a MuVi effect. Does that mean you have to actually cast the wizards communion using Mu Vi or is it just an arbitrary designation to express the Non-Hermetic mechanics of the total wizards communion level from all participants to double the desired spell being cast? If you need to actually cast with MuVi it will be a long while before my would ever be involved in a Wizards Communion, which seems to rather negate the point of free Wizards Communion unless every Mercurian is supposed to be a MuVi specialist.
Hmmm. I'd forgotten about that (and it does seem a bit odd given I don't think they have any cult lore and it explicitly says on page 114 of Mystery Cults that the Cult of Mercury doesn't practice initation).
I'm not sure we have a "standard" Pre + Mys Cult lore, but for the Neo-Mercurians, I'd suggest a total of +7 or +8? The Cult of Mercury is going to be a lot lower, given you're essentially just relying on Presence.
You have to actually cast it. You do have a bit of leeway due to only needing to be within 10 of the level of the Communion to get it to successfully cast. I think we're assuming that you get a sun duration rather than a momentary duration spell with Mercurian Magic, so that it actually works with rituals.