Most new worlds and west africans do best in pairs because they are monogomous breeders.
This doesn't mean you can just go out and buy two fish. They are often selective with tankmates, so giving them a choice is a good idea.
The best way to do this is to purchase more then two (one male and two females, or 4 random fish of you can't sex them) and once a pair forms, return the remainders.
You can also keep them alone, but you'll be missing out on the unique relationship of monogomous cichlids that make them so charming.
Keep in mind not all are pairing fish - but all the ones we're talking about are.
You can do 3 pairs, but I really recommend two, this way you have space for more non-cichlid tankmates, like catfish, and the fish can create territories of a more natural size. You can do kribs and keyholes.
Any tougher tetra will work well to fill in the upper levels of the tank, you have quite a wide selection, just avoid tiny or delicate species like neons. Danio's work well too.
I hate to hear generalizations on 'Africans' because 'Africans' covers an incredibly wide variety of fish. Some africans will tear plants apart, others will live with them without a problem. Generally in the case of the fish we are discussing, they may dig up plants where they nest, but will otherwise leave them alone. Keyholes shouldn't disturb them at all.