Front line:
Race/Class: Human/Knight.
Traits: Muscular and Skilled.
Skills: Athletics, Armor and Light Weapons.
Race/Class: Human/Barbarian.
Traits: Muscular and Skilled.
Skills: Athletics, Armor and Heavy Weapons.
Back line:
Race/Class: Human/Alchemist.
Traits: Agile and Skilled.
Skills: Alchemy, Firearms and Accuracy.
Race/Class: Human/Wizard.
Traits: Strong Mind and Skilled.
Skills: Concentration, Fire Magic and Air Magic.
Works well so far. At first I tried a build with a battlemage in the front row instead of the barbarian and a rogue instead of the wizard, but that wasn't going anywhere.