im thinking a nice asian arowana, gator gar, spotted gar, red tail catfish, clown knife 6 tinfoil barbs and 6 silver dollars. All of which are of the same size. and grow them together?
RTC might be a little too much for these Aros to handle. Same with Gator Gar. Please consider smaller catfish such as Tigrinus or Lima and Spotted/Florida Gars instead. The Gator and RTC would turn anything else into a feast.
I think it would be best to start with the aro. Grow it to atleast 12-14 inches and then add the other fish. I dont think adding an RTC is best, but if you must be sure the aro is over 16 inches before trying. RTC grow so rapidly is would so very upsetting for you to watch the RTC have a arowana snack. Should be a very cool tank, best of luck.
RTC,gator gar would eat the tinfoil,silver dollars and the others that would fit in its mouth and asian aro would be little too small for the full grown gar/RTC