Its my understanding that the standerd rule of thumb is 1inch per gallon of fish. While setting up a tank I commonly use calmer mubunas (trios) and peacocks (1 per color morph). Like the acei, yellow labs, white labs, and then pick male peacocks out. Stay away from the more aggressive mubunas Johnnies, demasoni and kenyi. You will find the lithobate male will problably be the biggest fish in the tank but adding one male and then mubunas and maybe another center piece hap or peacock would be great. Keep in mind the max size the fish will grow as you don't want anything over 5-6 inchs as its really to big to be in a 55. I always stock the tank based on max size and then add 10% more expecting a few to die off for a number of reasons... so if your following my guide line your starting stock should be 15ish fish give or take one. 4 trios and 3 peacocks/hap or 3 trios and 5 peacocks/haps.
on anther note always try to pick a selection that complements each other.. If you get cobalt's then stay away from an electric blue ahli.. the bright intense blue from the alhi will make your powder blue cobalt looks bad. Or a malrie peack with electric yellows... another reason not to double up on the color combo like that is lack of diversity in the tank if all you see is yellow and blue it looks a little redundant. so a nice lithobate (blue, green, yellow/red) pending what type you got, would look very good with an electric blue ahli iceberg or a ivory moloto, and then find a nice red peacock (dragon blood, german red, super red empress, rubescens, orange lemon jake)