We can vote on Nightmare vs Hell difficulty, but then no undecided votes, we pick either NM or Hell. If we have vast majority for Nightmare, we can then move to it. As for mana issues, only character with a problem is barb, his mana potions restore only 150 mana. As for necro, playstyle can be a bit less spamming spirits than on hell and he should do just fine with 300 mana per potion.
Problem with bowazon in ffa is she has way too many hard counters while she doesn't really counter anything. She either has slightly favorable odds of winning or no chance of winning, assuming similar playing skill and gear.
Problem with any barb is he is simply too weak and skill intensive to be able to kill consistently. Bowazon can spam arrows and kill something, barb can't just randomly whirl to kill, he has to actually namelock stomp to kill. Even then vitality casters usually require several stomps and against block you can only pray. He is meant to be played patiently and slowly, not like a barbarian. Either that or be the first to die out there. BUT, if played patiently and slowly, then he is dangerous. Not too easy to kill for high HP and requires one mistake to take 75% of your life in whirling.
Fire trapper is strong, although not close to LS variant in damage output nor range. LS trapper can use only LS as a trap while fire trapper has to use LS for some stun on range because WoF DOESN'T go through the pond and can't damage nor stun reliably. You have to play aggressively and stomp more to kill and can't rely on your traps alone to kill like LS variant can.