To put it plainly many of those fish will cross breed, that dramatically effects aggression levels and honestly I don't consider a 55 gallon a tank that any real cichlid community can ever healthily mature in. Min for me is a 75 gallon that added depth goes a long way but I've found that something like a 110 tall would still feel cramped with more than 10 adult cichlids the size of the ones you are talking about. Its really hard to keep a true cichlid community made up of the more aggressive species like the ones you have listed in a tank that size. I've had more success keeping Tanganyikan cichlids in smaller tanks under 100 gallons. If you get those fish they may be fine, for 6-12 months but once they all mature I've found that you loose a fish every 3-6 months from aggression until you have a core group of 5-10. Honestly my greatest success with cichlids is keeping dither fish. I use mono's but I've seen giant danios, or tiger barbs work fine depending on stock. A small school of 5-10 of such fish depending on tank size seems to do lots to soak up ambient aggression. I still feel that the stock and tank size will not work out as planned in the long run.