Hello rifdi.

Bettas can be put in community tanks. However, there are several fish to be avoided as tankmates for a betta.

1. Zebra danios - zippy, and may fin-nip the betta
2. Tiger barbs - definite nono, nips bettas
3. Guppies - contrary to what bobo said, bettas should NOT be kept with guppies. This is because the betta often mistakes the long flowing fins of the guppy as another betta.

Most bettas are only aggressive towards their own species, or as i just mentioned, similar looking fish like guppies.

As to filtration, bettas do not do well in strong currents.

I would disagree with your setup of 1 betta + 2 gouramis in a 5 gallon. Gouramis should be kept in nothing smaller than a 10g. Besides that, both gouramis and bettas are Anabantoids, and may be aggressive towards each other.

P.T.