I had 4 and two females in a 110usg community tank a few years back with a load of other gouramis and rainbows with to problems. I've had various gouramis over the years the only aggression issues I've had with any of them is the giant I have now. I can't see an issue with something like a 55, if your still worried make sure you add some hiding spots just in case of any trouble
since this is something I want an answer too rather then start a new post I figured I would bump this one.
I have a planted 20 gallon long I am considering setting up as a more Asian biotop. Do dwarf gourami's eat plants? I also want a school of them how many would I need to difuse territorial aggression? Like cichlids, I am thinking I could keep 6-8 of them in the tank. I am not planning any other fish but a siamese algae eater for this setup. seems everyone that has problem is asking about keeping two or three in the same tank.