Angelfish and silver dollars both do better in groups, and silver dollars get a bit big for a 55 gallon. If you're not too attached to it, I would get rid of the silver dollar and get 2-3 more angelfish. Also, keep in mind angelfish are very likely to eat the blue neons, as that's their natural food source in the wild.

I know nothing about catfish though, so MeTree will have to weigh in on those.

Edit: They will leave the black neons alone.