I had kind of the same idea after completing the game. My second playthrough is shaping up this way: Pallegina- Tank, running DR aura
Eder- Melee DPS, dual wielding sabres. It feels so classy! Plus he could use a break from tanking. He's my go to off-tank, still. PC-Bleak Walker Paladin. Running Accuracy aura with a reach weapon (Pike). This gives the aura to everyone (usually).
Hiravais-Reach Melee (Quarterstaff). I try to keep him in melee and using his werewolf ability often. Aloth-Back line, roleplaying as a pyromage.
Grieving Mother- General backline cipher. I'm really just using her because I got her too late last playthrough to progress through her story.
Generally it works out 2 close combat, 2 reach melee, 2 ranged (with Aloth constantly running around to maximize the angles on the fire spells). It's pretty entertaining. If I didn't have the story consideration for Grieving Mother, I'd replace her with a Barbarian just for giggles.