I guess I'll have to take that risk.
I mean, I can't think of a better party that actually fits my tastes.
If I make Firion a fighter, then Maria will have to act as a white mage (even though she's obviously a black mage, seeing as her Intelligence is rather high), because Gus really isn't supposed to be a mage at all; it's obvious that he's the main physical fighter in the party, and making Firion a white mage just doesn't feel right either.
It would've been much easier if Gus were another mage-type character; in that case I'd instantly make Firion a fighter, Maria a white mage (well, I like to use ladies as healers) and Gus a black mage.![]()