You have some wonderful options, with soft acidic tap water (like mine). But I would not include a Betta in a community tank. Some have luck, others don't. Betta can be very aggressive to other fish; they deserve their own environment.
Leaving out the Betta, in such a setup Cardinal Tetra
are ideal. They do not require swimming room, need soft water, love lots and lots of plants (they have a light phobia and stress out under bright light) and are a perfect match with the Brilliant Rummynose Tetra which is the most beautiful (and most often seen ) species of the 3 rummys. Both these fish do well in larger groups than 6, I would go with 9-10 minimum cardinals and 12 rummys. Rummys actually do not fare well with less than 12, they are probably the most "schooling" of the shoaling tetra fish. I have 20 in my 115g, a combo of two species Hemigrammus bleheri
(the Brilliant) and Petitella georgiae
Other possibilities would be five corys for the substrate, or perhaps a Farlowella (singly or a trio). This is a real eye-catcher but without soft water almost impossible to maintain. You can check the thread I started on my trio spawning multiple times.
In a taller tank the pencilfish Nannostomus eques
is an interesting addition with its 45 degree angle swimming; check the profile for more info. A group of 6-7.
On the plants, Water Sprite
floating is very good, for shade and the pencilfish browse the roots continually. I would hesitate over Wisteria
though; in a tank like this some more permanent plant (rather than one that need constant weekly pruning) would keep things better settled. Check out the swords, Pennywort, Pygmy chain sword
for the bottom.
Hope that helps.