Two cichlids willl probably be fine in a 30 gallon long aquarium which would provide ample room from them when they reach their max size to stake out territories to live in. However, everyone i know can never stop at just a few fish, and you'll probably be the same. So a 55 gal aquarium would hold a breeder (1 male, 3 females) colony of electric yellows and a Synodontis catfish. You can probably put a few more cichlids of similar size in a 20 gal for now, and just move up aquarium sizes as the crowding increases. This eliminates the expensive larger aquarium and filtration purchases until you're ready. Also only a few inch long cichlids would hide forever in a 55 gal. Good luck with your cichlids. When I was a young kid they were my first fish I rasied on my own, and they have some of the greatest personalities. When they figure out you provide their food they become puppy dogs.