I'll be honest, I struggle with companion stories. It is probably because how I put every magus, for the most part into their own silo story, which allows players to progress at their own speed, without waiting on another player to move things along, or for me, as the SG to move a player's character along. When every player has a story that is largely their own, neither of us has time to focus much on companions. All that being said, companions are a much needed thing to flesh out a covenant, so we need to find a compromise. My suggestion is simply that companions may not have major story flaws, and any minor story flaws need to somehow, some way, tie back to the covenant in general or a magus in particular. This can limit their ability to get 10 points in virtues, true, but when I build companions I sometimes find it difficult to get to 10 points in virtues, anyway. Without a major story flaw I don't feel that there is an expectation from the troupe or the player that the character has to have stories, and it also acknowledges the idea that a flaw without consequence isn't really a flaw and shouldn't grant any benefits for being taken. Does that make sense and also seem reasonable?
Let me caution you, as I did thompsja. Jacks of all trades are difficult to play in Ars Magica. I've tried, and I've always been underwhelmed by the process. It's also a trap for new players to Ars of examining the totality of possibilities and saying, I could do everything interesting, eventually. The trouble is that the interim is dull and boring, because the character doesn't have anything he excels at. Even a freshly gauntleted character can excel at things that magi 30 years his senior are just now beginning to understand. Being able to cast Leap of Homecoming, without fatiguing oneself at gauntlet is pretty powerful, and allows one to take Wizard's Leap, master it for fast casting and cast that spell without fatiguing oneself, too. That's just an example of what is possible. I recommend picking a Branch of the Arts (some may SWIDT) that interests you and pursue it to the near exclusion of everything else. You might counter that it leaves you weak to other things, by not knowing several other Forms, but my experience in both play and in storyguiding says that this simply isn't the case.
I will say, however, that since I tend to silo each magus into their own individual story, the impact on generalists is less than in traditional sagas where one or two magi might go on a story together, and in those cases, the specialist nearly always outshines the generalist. And if they're all specialists, they get screwed when a situation arises that highlights their areas where they lack expertise... 
I've played the utility magus, and I can say that I didn't enjoy it. I've played multiple specialty magi and have enjoyed every single one of them.
In regards to character building, let me also add, if you're familiar with any of the super hero RPGs that Ars Magica has far more in common with them with respect to designing characters than it does with say D&D. But even D&D made multi-class characters somewhat weaker overall than single class characters.
Also note that Trogdor's character Galan has a magical focus on teleportation. Per Arthur, a longevity specialist isn't bad. Or you could play a butt-kicking Flambeau, going to Scandinavia to adventure.
Sure works for me. Anyone wants his magus to have a regular companion?
For Bartholomeus, I already have background that says one of his "grogs" was a sweet-talker who convinced a bunch of people who'd been rejected by society to join him under the protection of this clumsy magic practitionner (not that he described it that way, of course). And to now follow his master to Finland. Does that ring anyone's chimes as a companion?
I'm good with Jonathan's suggestion - it's going to be slow enough without other characters. I was thinking that we need an agent as a companion. This might be a venditore that we share (since neither of us follows Verditius convention). He goes out purchasing rare items we need for our labs, and incidently mentioning that two capable Verditius could be interested in accepting commissions.
That's certainly a possibility. But do we want to advertise ourselves and to whom? My understanding is that we were moving away from the mainstream Order to protect ourselves from the plague. So advertising within the Order runs the risk of revealing our location. Selling to mundanes remains a possibility, but even there is seems like this would be a fairly limited market.
That raises the question: To what extent are we planning on isolating ourselves?
I had thought that the idea was to keep a fairly low profile. (Well, as low a profile as a covenant of magi can keep.) 
Let me point out that Scandinavia is outside of the Order, and moving up here is, somewhat by definition keeping a low profile. I suppose it becomes more of a question of how low a profile do you wish to keep in relation to mundanes, faeries, and the magical traditions native to this region...
I see plenty of magi doing things with Rego and Muto, with Terram extremely well covered and Aquam, Corpus and Vim to some extent.
Pyrale's interest in longevity suggests maybe a Creo focus.
I will look at Perdo concepts (maybe Perdo Vim countering hedge magi, or Perdo Animal magical monster slayer?) and Intellego concepts (studying the disease and scrying outside the Order's borders) over the weekend.
Back on companions - perhaps we should write them to be shared rather than owned by one player. Or make them up as grog level first and see which "develops" into a full character? That way the promotion matches the thread of the story being told. That approach needs a little hand-waving at the time of promotion though.
Note that Pyrale didn't express any special interest in longevity. This was a suggestion from me when he expressed interest in Corpus. You are correct that his latest posts suggest that his magus will have a fair concentration on on Creo. 
On covenant setup ... as we are outside the Order tribunal borders there is a hook for that which we should take, and most of us will be seen as odd or potentially a threat. Not sure how we "stat" up that difference.
Low profile is better but we need to also exist. I thought these boons and hooks might be a good place to start?
Site - Boons, Minor : Aura 5, Healthy Feature (fresh ocean breeze), +1 aging bonus. Seclusion (remote coast),
Haunted (former Magi and inhabitants), Fortifications
Island (free), Small Tower, Wooden (-1)
Income sources: Fishing, Animal furs, Timber
Vis Salary, requires agreed service each year to gain share in Vis.
Hunters and Fishermen (free), both hunters and fishermen have been employed to live at the covenant and work as part of the income sources - Furs and Fish. Goal is to have enough produce to provide income sources above the needs of the covenant.
I have no problems with any of the suggestions. Moreover, it has the two things I really want: an Aura of 5, and a Healthy Feature. Any other hooks/boons that are desired?
I was also thinking of a Regio, either the type we have control of that allows the covenant to have more "space" than it appears, and also a place which can be anchored to the Magic realm. There are a few options depending on how friendly the region is.
I can write something up in more detail if it's acceptable.
I simply read through Covenants to see what Boons and Hooks caught my eye, so these are just random thoughts.
For the Site, I think our boons/hooks should relfect our remoteness:
- Aura (minor boon): Of course, everyone always wants a great aura.
- Difficult Access (minor boon): The covenant is probably somewhat inaccessible. We discussed an island, for example, and that would qualify (particularly if the coast is a bit rough).
- Healthy Feature (minor boon): Sure, we always want something posivite to live a long life. On the other hand, perhaps Hostile Environment is more appropriate to describe the location?
- Seclusion (minor boon): Finland certainly qualifies!
- Vast Aura (minor boon): If an entire island is covered by the aura, this might give us plenty of room and flexibility to develop the covenant. That would also reflect a place at the fringe of the Order.
I don't see us as needing large Fortifications, since our remoteness would make it hard for us to hire mundanes, while at the same time safeguarding us from mundane threats:
- Island (free): If our island is very close to land, along a river or in a lake istead of being in the open sea.
- Small Tower (free): I don't think I'd go with this, but if other people insist I don't have a particular problem with it. Such a tower is too small to contain our labs anyway; it is more of a safety feature against mundane attacks.
- Crumbling (minor hook): Perhaps we set up in a fortress previously occupied by magical creatures, like giants, that were driven away long ago? This would certainly be poetic for a saga about the fall of the Order -- can we rebuild something out of the rubble?
- Wood (minor hook): Certainly seems appropriate if we built the location from scrap, as wood is the most available material. But with several magi who are good in Terram, how long would that last?
Our remoteness will certainly need to be reflected by the nature of our income, but otherwise I don't see us with many Resources boons or hooks:
- Vis Grant (minor boon): I don't think this boon is relevant when there are no NPC magi controlling the covenant.
Our Resident mundanes are probably limited in nature:
- Hunters or Sailors (free): Would certainly qualify. The second one only apply if we are on the coast.
- Inhuman Residents (minor boon): We could have taken the lead of some magical inhabitants that lived at the site. Perhaps a race that was formerly enslaved by giants living in that crumbling fortress? There are many possibilities there, like dwarves, magical animals (maybe even magical hares like Garapadax, Bartholomeus' familiar), or something else.
Surroundings would also be conditioned by our remoteness:
- Minority (minor hook): If most of our covenfolk and grogs are Christian, while the surrounding area is pagan, this might generate some stories. No overly interested in this, but this might be appropriate.
- Missing Expedition (minor hook): The site might have been formerly settled by Hermetic magi, but they disappeared/were slaughtered. They may be the ones who killed the giants lving here previously, but were in turn attacked?
Realize that Thyra knows CtMT and will have vis to put some up at the start. My story set up has the Tremere to to have scouted the area.
I'd like to see more discussion about this from the troupe. This is, your covenant, to be frank. I'm fine with the players designing it to be their magi's home. There's no reason to believe that they hadn't been able to conduct sufficient reconnaissance and survey operations to select a suitable site.
Now that it's raised as a topic - How we start is important and I have mixed feelings about the site having such a strong link to an individual character. It depends if your Tremere hook is actually a hook that we all will need to deal with so to speak. If we just accept that the Tremere quasi gifted the site what are they going to want in return? Or did they not really know who or what was out there, and dumb luck and group effort found it?
Just as likely too that Agnarr has been scouting the region too.
It is not tied to a character or House. The Tremere scouted the area (being pragmatic). They might have scouted it decades ago. It was a hook to make it easy for a group to show up, outside the Order, with no previous knowledge of the area, and find vis sources.
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