I would take back the other corries (or go to 4-5 peppered) and just keep a conspecific group. Personally, I would go with a group of sterbai, panda, julii, or aeneus(bronze or albino) as they tend to be of the more active variety.
In the 6.6 you could probably go to 4 pandas(as they tend to stay smaller), and the betta, and take back the frog(may be a bit too much bioload). Makes for a pretty color combo with the white/black and a colorful betta. May want to up to a AC20 filter. You could also consider taking out all the fish other then the betta and go with 6-10 pygmy corries.