I'd go with a group of 8-10 of one of these Thorichthys species:
helleri
mixteco gold
pasionis
mixteco blue
These are all gorgeous fish that will grow up to around 6" or so...not huge but will be beautiful once they reach adulthood. One of the problems with all Thorichthys species besides the firemouth is that they don't show much color for up to a couple of years, but after that they are all STUNNING. I've been to Rusty Wessel's fish house and he has tanks with adult specimens of every Thorichthys species and these I listed above are my favorites. Personally I'd probably go with helleri.
You could do that group of cichlids, a nice group of some type of livebearer (I'd do platys) and the plecs and have a beautiful "almost" biotope tank...I say biotope because the plecs are not central american..lol