If it was me it would be a wild betta tank haha.
But otherwise, I would probably do a biotope style set-up for a decent sized group of pseudomugil mellis. I am really peeved I sold mine and wish I could get them back.
I would put river sand down, buy a packet of riparian leaves from Dave and put these all over the substrate. Then I would see if you couldn't find some tea tree roots at one of the fish stores in your area. If not, I would use grapevine to give it the sort of 'roots going into water' look.
Any plants would be Australian natives, but since I am not a big plant user I would probably just have it non-planted.
Something that looks like my old mellis tank.
This is just my opinion however. I am not a big fan of tetras or rasbora or corydoras or many of the more popular species of fish. Therefore, my tastes may not run to what you like.