I love cichlids, their behavior is interesting to me. One thing you have to remember is, they are aggressive and they will kill one another from time to time. So be ready for a dead beat up fish every once in a while, and chances are it will be your favorite fish that gets killed.
Introducing new cichlids to the tank can be very difficult. My fish will usually give the new guy and "initiation beating" for the first day or two and then leave him alone if he hasent succumbed already. If it seems to be getting to rough, the fish getting the beating should be removed to a hospital to recover from the stress and injuries, and then attempt to reintroduce later.
My Flag Top recently just killed my Hongi. I didn't see it coming either. I had just been watching the fish and they were peaceful towards each other, and then an hour later and the Hongi was dead, and the Flag Top was colored up and dominating the tank. Then, the same thing happened among my Yellow Labs, and my favorite lab was beat up in a conflict, it was frustrating.
I think one you have an established group of fish, your good and shouldnt have too many aggression issues, unless a cichlid at the bottom of the pecking order is trying to make his way up...then you got problems