To answer your question about knowing if they are all males, I made sure I bought one that were already coloring and have their egg spots, also I went to a very good LFS that deals with only monsters and cichlids.
Yep Afro is so correct in all male setup your fish will form a pecking order and so on and even if you add more males there will always be the one or two at the bottom of the list that will get the short fin of the deal..
With placing more males there is the chance for the spreading of the beat downs.. cichlid aggression you gotta love it i know i do..