African cichlids could be very hard to keep happy. If your water conditions aren't perfect it will affect the aggressiveness of the fish.
It's a must to have plenty of hiding spots. I would be careful with overstocking the tank as at first the fish will be doing fine then slowly the weak will be killed off after territories have be established. Crushed coral is a good substrate for them. I found having just a couple of fish in a tank that size to be better than a lot.