Really it all depends on the personalities of the fish you have. I've had as few as 4 in my tank at a given time (Daiquiri was in time out for a while), and they've gotten along just fine. However I've heard other stories from other members that have more aggressive fish. Really, you'll learn what works best for YOUR fish based on your experience with them. Don't expect to get it perfect the first time, something is always going to go wrong, just be ready for it when it does.
Winston~ Damian~ Twitch ~ Evans