I would be concerned that the labeo bicolor would get to large for a 20 gal. Also being such a semi-aggressive fish, it may pick out a victim and harass it constantly.
No RTS in a 20g tank, that is wayyyy too small for them.
Your options are rather limited if you decide to keep the gourami. Being a tall tank you have less surface area for oxygen exchange. If you want to keep it the way that it is I would add a few dwarf cories or some snails and shrimp.