From the perspective of tank size (length and volume) that's fine, understocked in fact. For the benefit of those of us who think in imperial better
this is a 3-foot tank of roughly 25 gallons.
But you have a major problem with the Betta. I can all but guarantee it will eat any Boraras it sees. Betta will eat neon and Cardinal Tetra
too (mine did), and they are larger than Boraras.
You can also thicken the planting a bit. For the fish mentioned, open spaces are not necessary because they are not active swimmers. Boraras species and Cardinal Tetra
prefer to cruise around thick stands of vegetation. Floating plants are mandatory, as these fish also dislike overhead light.
Leaving out the Betta and staying with the rest, you could have another group or two of a smallish shoaling fish. Pencilfish, hatchetfish would add interest, and they share this type of environment. Substrate fish (otos are not substrate, they spend most of their time up in the plants, on wood, etc.) like corys, Whiptail Catfish
and Twig Catfish
would add bottom interest, though with the latter I would not have otos too.