Another perspective. A 55G can work for 3 species of mixed gender mbuna. Avoid yellow labs with red zebras...they will crossbreed even if you are not trying to breed. Avoid kenyi in a 55G. Definitely fill the tank with rocks. Think in terms of something like this:
1m:4f Metriaclima estherae red zebra
1m:4f Cynotilapia sp. hara
1m:4f Labidochromis caeruleus Nkhata or Labidochromis sp. Perlmutt
No need for scavengers if you don't overfeed, but if you want a bottom dweller I would stick with Synodontis lucipinnis (sold as dwarf Petricola) group of 5.
1m:4f Metriaclima estherae red zebra
1m:4f Cynotilapia sp. hara
1m:4f Labidochromis caeruleus Nkhata or Labidochromis sp. Perlmutt
No need for scavengers if you don't overfeed, but if you want a bottom dweller I would stick with Synodontis lucipinnis (sold as dwarf Petricola) group of 5.