Research is the best advice. I have just done what you propose - taken a tank that has been running for years and converted it to a cichlid tank. I went to the LFS, got advice. I showed the store staff three or four colorful fish I thought my daughter would like. He recommended three species to try, but only two combos. I gave that list to my daughter. She decided on Yellow Labs and Demasoni, both mbuna from Malawi. She knew that the demasoni had to be kept either singly, or in a group of a dozen or more to atempt controlling con-specific agression.
We bought 8 yellow labs and a dozen 1-1.5 inch demasoni. One demasoni died in the bag on the way home, four more died in the next 5 days. Water quality is excellent. One yellow lab died as well, looked in good health.
So now we are at a crossroad. Double down on the demasoni and add more to try and spread out the agression, or leave it alone and see if we end up with only one. If I had it to do over again, I would have skipped the demasoni, but perhaps I am judging to quickly. they are intereting fish to watch.
It helps that I have 100 lbs of texas holey rock, lots of nooks and crannies for fish to hide in. It also helps that I have two fluval 404 canister filters and a push-button water change system, so I can overcrowd the tank without letting nitrates get high.