Really, with the stocklist you've got you should be able to go any direction you want.
I honestly am not a plant person despite myself.
But for stocking suggestions. . .
Rasborras, neons and the danios like friends, lots and lots. Not sure what rasborras or danios you have (harlequin, galaxy, giant, zebra etc), but I'd get rid of whichever species gets largest or that you like least. Then I'd add ten more of the other two, so that you've got two schools of a dozen each.
Since this is just a temp home really for the balas, I won't address them.
Then I'd add bottom dwelling fish; a small peaceful species, like a few kuhli loaches (most other species of loach will outgrow a 30G quickly) or a few small corydoras (Species that stay under 2" preferabbly), or a small pleco (A species that stays small, rubber lip, bristlenose, clown, etc). If the tank is really established and has lots of algae, maybe even some of those darn fragile ottos.
Then, I'd add a "feature fish", optimally something that won't be bothered by fast, frisky danios or rasborras, but won't outgrow the tank. Maybe a dwarf gourami.