You can watch my wife and I play our short lived series
We just use models from all ranges, but mostly Gamesworkshop from recollection.
I personally feel that the more aggressive spellcasters level up the fastest. They always have a reason to cast spells. Hence, Elementalists tend to level up quickly and end up really deadly.
https://www.youtube.com/watch?v=YYy8tdohXsM&index=5&list=PL9P_t8L3FFApCLhnnx54rmntxxlfVKiv7
In Frostgrave you choose your wizards Main School, but you get a good chunk of spells from Neutral and allied schools as well, making a well rounded wizard. I really like Illusion spells and Soothsayer, personally.
In regards to your warband, I'd say go with the Bretonnian Damsel. Mouslings and Elves don't really have the "Frostgrave" feel in my opinion, though they really don't say what race creatures are in the game for the players. . . I just picture the warbands as human, as that's how the rulebook sets them out. That, and the Frostgrave North Star Miniatures representing the warbands look closest to Bretonnian Peasants or Empire Free Company soldiers. So, Lore wise, the Damsel's warband is going to look closest to what I think a warband would be. And the Damsel can be whatever magic background you choose. Thaumaturge may be the closest to what I see a Damsel doing in Warhammer Fantasy,(that is, buffing and healing the soldiers of Bretonnia) mixed in with some other schools of magic, for kicks!
That's just my look on it, though.