Well, I can tell you about the Ars Magica angle for this one, as I have played that for a number of years.
In that game you have two "primary" characters, your Magus and your Companion. There is also the "Grog Pool" -- semi-NPCs, often warriors, but sometimes now, who are not anywhere near as powerful. In any given adventure you run either your Magus OR your Companion, only very rarely both, and equally rarely only a grog. Each individual grog is not played by a given player, but rather by whoever feels comfortable using a specific grog in a given adventure.
Okay, that is the general background. Now on to play style.
If you are running any sort of troupe-style game, remember that each character will play less often. Rather than being in every session, a given character will probably only be in about every other session. This means they will probably advance more slowly.
Another aspect is that in troupe-style play you have a wider variety of characters to draw upon, thus allowing the group to "tailor the party" for each adventure. As such, it is a good idea for each player to create rather different characters. If Character A is magic-based, create Character B as a physically-based individual. If one is urban, create the other one nature-driven. The point is that by creating somehow diametric characters each one will feel appropriate at different times, thus you will feel encouraged to play both of them.
Create a base. Don't just have all of your characters wandering freely. This "base" could be as wide as a city in general or a forest; on the other hand the base could be a single building (or set of buildings). Essentially you want to know that there is A Place where you can (usually!) find the other characters in case you need to "swap out" characters. Often D&D encourages widely wandering parties with no significant ties to a specific locale; if you are going to have a reserve of characters, you'll want to know where to find them!
What tends to happen in troupe-games is that the GROUP becomes an extra character. Since you are not tied to one character, you start thinking about how your character's actions reflect on the group in toto. You might well create and/or buy magical dingi for the good of the group (or their base), rather than for a specific individual. This also tends to reinforce the sense of community. In other words, players eventually think about the progress of the group at least as much as about the progress of an individual character.
So any of these points could be seen as a positive or a negative, depending on your take on it. I have loved troupe-style play (even troupe-GMing! -- I'll post more on that if you are interested). I know other people who cannot stand it. Obvsiouly my response is coloured to look more on the positive side, but if you haven't done it before, give it a shot. I think you'll enjoy it.
