Remember that cichlids are territorial and will attack each other and other fish if the tank is not big enough for them to define their own territory. Going on that you will be using the 55g as the cichlid tank i wouldnt suggest more than 3 species of african cichlid with a pair or trio of each species (depending on the breeding habbits of the individual species) no more than one species of central american or large south american cichlid (either a pair or a single fish depending on the species) or no more than 2 species of dwarf south american cichlid (again numbers of depending on the breeding habbits of the individual species).