I am winging it using the Mythic Pound of silver, and historic knowledge that gold currency is limited to Iberia, Greece, the Islamic world, maybe parts of Italy, and parts of Africa. I am also using a website I found the other day, titled "Understanding Old World & Medieval Currency". From that site I have:
Doesn't have to be perfectly accurate, just plausible enough. Hard accounting is done in Vis anyway.
This raises a question I've had for a while. When the rules say "a Finesse Roll," is that (1d10+Finesse) or (1d10+Finesse+Characteristic)? I can't seem to find anywhere in the core rules that specifically says what a Finesse roll is. I'd always assumed you just added Finesse. But I'd be more than happy to learn that I was wrong and that you added a characteristic (like Int) to the roll as well.
I ask because you said that the lowest Vocis could roll on a Finesse roll is 10. Since his Finesse is 6 with a focus on Imaginem, and the lowest you can roll on 1d10 is 1, that leaves 2 points unaccounted for. Is he adding Int to the roll?
Have Fun!!!!
I would suppose the Characteristic would depend on what you are doing and how you are using magic to do it. An Aimed Finesse roll would be Dexterity. Fabricating illusions or material objects would be Perception (or maybe Intelligence?). Fast Casting involves Quickness.
Just guessing.
The Fixer knows the answer, I am sure 8)
Aimed Finesse rolls are Perception+Finesse (page 86 of the core book)
Creating things with Rego magics is also Perception based.
Creating with Creo magics use Int+Finesse.
Fast casting is Quickness+Finesse.
There you go 
Mister Link beat The Fixer to it. Yet I shall still await his confirmation and judgment, for such is the authority I have invested in him.
Marko?
It's a mess.
It always add a characteristic, but it depends on the situation. Per to hit, Qik to fast-cast, and for the quality, it's either Intelligence or Perception. Callen and I had a small discussion about it once, on these boards IIRC, and it seems that there's some consistency to it, but I can't recal what, if any.
There:
That'd be Int for Creo, Per for finesse, mostly. Some of the time. If the stars are right.
As said on the other thread, 2 things are clear: Aiming uses Per, Fast-Casting is Qik.
Other than that? No hard and fast rule, and it's a mess.
I tend to agree with JL for Per/Rego and Int/Creo, but this is more a HR than anything else, although I believe Int + Creo was slightly clarified somewhere, probably in Societates.
As an exemple Callen found exemples of Craft magic using Int, I remember some using Dex, and I even think I saw one using Com 
At least, Int + Creo seems sturdier than Whatever + Rego . And there's the other forms 
Ummmm....
Which one is that again?
Heh, you have had rather an influx haven't you?
Bernat del Cavall is my companion character, a spy from the court of the Bishop of Urgell, fleeing for his life after he discovered that the Bishop is treating with the Fae.
Hm, that's a dev thread. I should post him as finished.
I was adding his Per, which is +2. My (apparently incorrect) assumption was that Per is used for all Finesse rolls, which is part of the reason Vocis's Per is higher than his Sta. It sounds like most of what he does is either Per or Int (also +2), so he's good either way.
Official generic AM coins are 10 to the pound, and gold trades silver at 10:1, so 1 gold coin is 1 pound of silver equals 10 silver coins.
which puts official weight of all coins at 1.6 ounces, if you want to try and factor in real world currency, though as noted previously, he gold exchange is off.
I don't know where any of this comes from. I am trying to find a source to site. ut in Ars Magica, it is 360 Mythic Pennies to the Mythic Pound. Gold trades to silver at roughly 16 to 1, more or less. Not sure on that, Ars Magica deals only in silver and not Gold.
What character or characters is he associated with?
None, a priori. He is a free agent seeking sanctuary with a group he has heard of in his professional capacity.
You might work out best picking up a job as a mercenary or a laborer. Wanna be a sailor? We can add you into Moonlight over Giza and say you had been a redshirt laborer working under Ximo and Jimo.
Hmm, I rather liked the idea that he deliberately got himself mixed up with this band of freaky magi; but I guess this could work too. He could be looking to flee the country, although with no magical transport he's a long way from home. Still, I could see that.
Would it be plausible for Bernat to have stowed away on Johan's boat?
I actually kind of like your original idea as well. I think Marko would be willing to run with it if you flesh it out a bit. Would he show up at the doors of the covenant, try to contact them via a messenger, or something else?
Selim would love to join this "buddy movie" 
Anything that entails travel and trading definitely fits within his interests. But, if you want to keep it a magi only thing, that works too.