What effect does it have, if one char is good or evil beside the fact, that Paladins won`t be available, if one evil Char is in the group?

Nothing in practice that I can think of at the moment.

Yeah, I don't think it has any effect in-game.
I had either a good cleric or a paladin complaining about me digging up graves in EotB2, but that's about all I can think of.

I read in the manual that some NPC will never ask to join your party if you're evil. I specifically created an evil party in EoB 1 game and the first dwarf was eager to join me nonetheless, or maybe it's because he was dying. I never checked any other NPCs for that matter.