I currently keep lots of gouramis in my community tank and i also have 1m 2f bettas in this tank also without any issues but i always buy my gourami's in pairs so they keep each other busy, so i have 2 moonlights, 2 opaline, 2 snakeskin, 2 yellow, 2 striped, 2 croaking and 2 pink kissers all with my bettas and never had a problem.
as for a plec get a bristlenose, Medusa Bristlenose (liitle bit bigger than a standard bristlenose and a wider head but much better looking), Rubbermouth/bulldog pleco or a clown plec as they are all fairly small and cheap, except the medusa's they tend to cost a bit more.
I also have a smaller community tank with fancy tail guppies and 1m and 3f betta's in and never had any probs