jfyi, many betta enthusiasts say a 5 gal is a minimum tank size for a betta alone. others argue that a 5 gal isnt enough and a 10 gal is the minimum, with maybe 3 corys, 3 otos, a couple snails, or a few shrimp. you should not put guppys or groumis with a betta since the betta can mistake guppys for another betta, and goroumis fight with bettas.
i think that 5 gals is good for a betta and maybe an oto or two, maybe a snail or two, or a couple shrimp instead of the otos, but thats jmo