If you are planning to just use the standard light with no ferts or carbon added, you could go with some java ferns and anubias tied onto rocks around the tank, and Marimo moss balls. Some java moss would look nice too if you can find it.
Instead of a dwarf gourami, I would go with a honey gourami because they are more peaceful and also hardier.
Tank looks good so far- good luck!
20 gallon high-tech planted