Labs or demasoni, yes - Kenyi, absolutely not in that tank size. Most mbuna will NOT work well in a tank that small. The only mbuna I would really recommend are the demasoni.
probably 2-3 pairs either labs or Demasoni. The best demasoni i ever saw were in a 20g breeder tank and Aqaurium Oddballs in Tulsa, OK. They were awesome. you should be good with 2-3 pairs of each or you could just do like 1 male and 2-3 females.
start with choosing what color you want... yellow, blue, red, orange and make a decision from there. A good idea is to go to a pet store and see what catches your eye, almost all africans mix well together. The sky is the limit, good luck!