Dwarf gourami and cardinals is what I was going to do in my 20 gallon before I upgraded and decided to go with cichlids and use that 20 for a quarantine tank. Another option for you would be to not get the gourami and replace it with an algae eater, bristlenose pleco are good for small tanks because they stay small compared to regular pleco's which get huge. In addition now that you wouldn't have the larger Gourami you can get some small shrimp which I think are awesome (the Gourami would eat the shrimp). Red Cherry Shrimp and Ghost shrimp are all cool looking, stay very small (less than an inch) help keep your tank clean and add another dimension to the tank. I would recommend the red cherry shrimp they aren't aggressive towards each other and look really cool! You could have about 10-15 of them in your tank.
In the end you have to be happy with it so choose what you want. Just some ideas. Good luck!