Stocking 20 gallon saltwater tank.?

I have a 20 gallon high aquarium and am waiting to add fish until i have the right mix. I know all there is to know about the initial setup as i have the proper water condition and live rock and sand plus lighting and a cycled tank. I was thinking these fish for the 20 gallon. Pair of tank raised common clown fish, 1 royal gramma, 1 firefish, 1 banggai cardinalfish. Is this good compatibility or no because ive heard different things about the gramma and cardinal. Also if you had to alter my stock list what would you add, subtract, replace?