Q&P and Crosswords, I believe are the most important. Mamya, I don't understand about CB? When I first joined, it was pretty much- anything goes. And also, anything that wasn't a "serious subject". It seems to be the opposite more recently that people say "should this be in CB", where it had been the default. I don't mind, but it's helpful to know.
As far as arguing goes- that will happen on any public site, about anything at all. Providing it doesn't become abusive, I think that should just be expected, that not everyone will always agree x