Ok, IMO seeing as your asking I'm gonna assume you are not to familiar with SA/CA cichlids?
Ebjd are VERY hard to grow out into maturity. I myself and many other exsperienced hobbiest have tried with mixed results.(never got any past 3-4").
I'd say try a regular Dempsey first as they are far more hardy. With that said. 1 Dempsey is the recommendation for a 55. Unless its a dedicated breeding pair in the tank I would not try multiple jd's with other fish. They can become very aggressive as they mature.
Convicts,Hondurans,fire mouths, are just a few of the med size that would also fit what you are looking for when full grown.
Oscars can be kept in a 55 for about a year but as they hit the 10" mark should be moved to a larger tank. (this goes for all the larger cichlids that hit 1'+ mark) the amount of waste and poop they produce is massive.(again all larger cichlid's).
With some of the less aggressive fish you could add senegal bichir, African brown knife, loads of different catfish you can chose from. That will all also go after full grown and baby guppies.
Lastly, I know the "feeder aspect" is what usually draws people to the SA/CA cichlids at first because it is "cool" to watch them in predatory mode. However... Feeders and even frozen is NOT the most healthy diet you can provide. The staple of any of these fish mentioned should be a quality pellet diet with mixed in "treat" feeders and frozen a couple times a week. Yes breeding guppies are more healthy then goldfish but again nothing will bring out color and over all good health as pellets.
Oh and another great food source to feed live.. Crickets. Cheap and MANY fish love them.
Hope some of this will help. Good luck. Post pics when ya get the tank set up.