new 135.

I would get a few Plecos. Sail fin or more colorful small ones- for the bottom. Definatley Corys or Synos, please Lupin and get a loach ;^)
Middle stratus- are you a big fish lover(oscars/altum angels), a colorful fish lover(fancy gold fish/discus/platies/mollies/guppies/glofish), or a busy body(danios/barbs/tetras)?

Top- upside down catfish, female bettas? Make sure you plant appropriately. I would go with Giant Vals, and float some hornwart.

Natural gravel with driftwood might look good?
 
A huge tropical community. Tetras, mollies, guppies, the works
 
I would not mix bettas and oscars. The bettas would be eaten by the oscar. And usually if you have an oscar tank, thats about the only thing that can go in it, at least last I knew.

But I'm always partial to large communities, in which bettas can co-exist.
 
chichlid or a giant tank of killies!1!!!!
 
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