Clown loaches, commonly grow 8-12" in the aquarium. (Correct me if i'm wrong) Most sharks get large to house in the aquariums also. I.D Sharks grow 3-4' or something like that (Again correct me if i'm wrong.)
Live plants are pretty much easy to take care of. Put some plant fertilizer (For aquariums) maybe a CO2 injector, lots of light, and watch them grow, and maybe some leaf trimmings here or their.
As for the betta idea. No. A betta would fight (and kill?) your gourami's as the betta will think that they would be competition for a mate.
Maybe a german blue ram? They are exotic, and very bright neon colours, very lovely fish if you ask me. They will get a little aggresive during mating time though.