I don't think getting cories for that setup is a good idea. They'll most likely get beaten up by the rams, especially if the rams breed, since a 20 gal doesn't have very much space. Otherwise it sounds fine, except that as modernhamlet mentioned, there might be some aggression between the gouramis and rams. It's hard to say whether or not it will happen, but there is a risk.
*shrug* Who knows? It can be difficult to predict the behaviour of variable fish like cichlids; some are more aggressive, some less. I wouldn't risk it though.