Dwarf rasboras...do you have access to those? They're usually very rare from what I've heard/read/seen.
I would get a minimum of three cories - they need friend to feel secure. If you would like a few more, consider looking for pygmy cories. They stay VERY small and are very active. I've got six and I love them.
Just be aware that they are NOT scavengers and need to be fed just like other fish. They need a wide variety of foods
You can get many more shrimp in that tank. They aren't usually counted against the bioload and it is often said that one per gallon is a good rule of thumb.
I do believe that black neon tetras tend to get a bit bigger than regular neons/glowlights. Cardinals are an option too.
Harlequin rasboras would work nicely.
If you want a really active tank...think about danios (but not with the betta). They are very active swimmers.
instead of a betta with the smaller tetras, have you considered a dwarf gourami? I'm fond of the neon blues variety.
Also, can I suggest a black background for the tank?
Just some ideas
