Firearms isn't too bad, but only for one weapon and it's only for like "oh shit I need to kill shit" moments. Damage is fairly low otherwise. Sadly, missile is also low, so mostly your options are to either throw bombs(don't need the throw skill for that either, just need to make bombs which you don't get many herbs for until later in the game) or get 2pt accuracy so you can melee from the back. That said I played with missiles and did fine, you really only need 2-3classes doing good damage. Alchemist only really need to hold herbs and run around. Get whatever for dmg, but if you don't use a rogue you might as well go dex dual wield daggers from the back, it does solid damage once you have good daggers.
Resist is fairly useless, it's good on a few key encounters but overall I'd rate it pretty low. Also the archmage set provides a lot of resist so your mage generally will end up with solid base resists without anything(I think I was capped in 2 resists from vit/willpower and other 2 at 60). This is especially true if you go Battle Mage with the additional resist. Insect with Chitin and/or Fast Metabolism would probably be better. Your mage can also generally cover 2 shield spells for elements, so you're only weak to a few things.
Get one mino in frontline, make sure to dump into dex and str instead of str and vit, you don't need the vit but you do need the dex. Will probably end up needing 1-2points in accuracy too. You'll get a bunch of bonus str from the skulls you collect(obviously get headhunter) and the higher starting str means you'll do quite a bit more damage that way. Other frontline lizard is fine, though you might as well Ratling for additional stats via mutations. Frontline resist isn't particularily useful as you might think since every elemental damage source is aoe and hits the entire party regardless, so the damage is scaled appropriately.
That's pretty much how I'd do the ultimate party based on my knowledge now, 1mino barb heavy weap heavy armor with a bit of accuracy, 1ratling barb heavy weap heavy armor with a bit of hp thing, 1 backline ratling alchemist light weapons dex with 2pt accuracy and 1 wizard or combat mage, fire/air with 1pt water and 3pt concentration for the various useful spells, insect most likely.
Finished the game, missed 3 secrets, but eh, that's not terrible. Great game.