Angels really are unpredictable. I've kept as few as one and as many as 7 or 8 full size fish. I'd agree with Ed that one or two individuals housed with a breeding pair will likely suffer the worst. It all depends though. I currently have two breeding pair (which have spawned simultaneously) and a single "loner" in a 46g tank and they're all getting along just fine, despite the overcrowding. Thankfully two or three are destined for my sister's tank soon.