I've got quite a few years behind me of keeping Africans. For a tank that size, your safest route would be to go with Tanganyikans such as julies, Neolamprologus, Altolamprologus and such. Mbuna (most of the cigar-shaped Malawi fishes) are exceedingly territorial for a 4 foot tank. Most people crowd them so that dominant fish can't single out certain ones to bully to death. This is much easier to pull off in a 6 foot (or larger) tank, but even then having a hospital tank up and going at all times is prudent. Some cichlids are more bark than bite and just run offending fish off, but mbuna can be deadly serious about any offending fishes in their territory. I really think you'll have a better experience avoiding those and sticking with Tanganyikans or even smaller peacocks.
Nothing good happens fast in an ecosystem.