Cardinals are borderline but neons are a no go once your angel/angels reach about 3-4" which will happen quickly with good food. They are predators by nature and neons are on the list. Mine even went as far as to eat ottos. I keep mine with rams, serpaes, x-rays and a few smell plecos.
Small fish will probably start disappearing at night if they are small enough. Only my personal experience of course. All fish are different.....
Well, they are cichlids!
Probably one just trying to establish dominance. I had angels many years ago and they would have showdowns every now and again, but there was a definite pecking order.
You can't tell males from female until they breed. When they do breed females will have a thicker and blunter breeding tube and the males will be pointy.
Don't worry about agression to much.
And those are platinums. Not sure what kind, but that is the general strain. Just like the ones in my avatar.