Mr. Fishman has given you some great advice. I tend to follow the one adult per 10 gallon philosophy as well. While nothing is set in stone, at least understanding the guidelines and reasons behind them help you make informed decisions. If we're talking young fish, I'd personally keep multiples more, knowing a new tank to split them up as they mature is in order. If that's not realistic, I'd stock young fish based on adult rules. I have a terrible case of collectoritis and impatience when it comes to my hobbies, so I know the urge to have a full tank now!
I have a heavily planted 65g display tank with 4 pre breeder angels (heavenly behavior) and a 55g display intended for 4-6 angels. Had a pair spawn in a small holding tank before I was ready to move into the 55 and their personalities have changed! Herding other fish, dominating anything that's a perceived threat, etc. Might need to revise down that angel count to 4 myself!