So I Have This Empty Tank..

[Zante]

I can't believe nobody suggested a shrimp tank!
Black substrate, couple of pieces of pink quartz, a piece of wood with some flame moss and a couple of marimo balls.
 
Add a few crystal red shrimps and soon you won't be able to count them!

 

[Ruskull]

A male sparkling gourami? Maybe 3 females too -MBOU knows how to sex them.

I would get another betta though, a local fish store has two that I really like, one that is fab with smaller fish, unfortunately I have Gouramis in all my other tanks bar my betta set up ;(

 
 
The words "unfortunately" and "Gourami" should never be used in the same sentence!!!