Dwarf gouramis are much less aggressive than most other gouramis and a 55g, esp. planted, should give them plenty of room to find their own space. If you add tetras avoid the smallest ones or you might lose them to the rams. You can also mix many of the types of corys so if you wanted you could use 3 spotted or peppered and 3 skunk corys to bring up the #s enough to make them comfortable.