well air pumps are the noisiest filters you can get. the xp1 is gonna be tons of filtration for a 20gallon, but yes it'll work, and be quieter than an airpump driven system.
Don't know enough about
RO units...but most freshwater tanks don't need them. If you can list your tap water specs (pH, hardness in
Kh and
Gh, and nitrate/phosphates) we can tell you if
RO is necessary, useful, or just a waste of cash.