Balas and RTS' are somewhat different. Balas are schooling fish that grow to huge sizes, we're talking 14" here, and if you have a school, then the minimum tank size is about 200 gallons to keep them happily.
An RTS however, will grow 5-6" and are solitary fish, they are aggressive and terratorial. If you're looking for a bottom dwelling fish, then an RTS may be the fish for you.
Note: Because of the aggression, I'd recommend adding the RTS last. Also, look out with the Corydora's, as they are also bottom dwelling fish.
With the two
DG's, I'd maybe go down to one as it's luck-of-the-draw if you get ones that don't fight. Often they fish to the death if kept together unfotunatly.
Welcome to FishLore! Good luck with the 55!