Is this fish tank overstocked?

I have 2 clowns and 1 green chromi right now, I want to add 2 mandarin dragnets (LFS showed me they accept pellet food) 1 more green chromi a pistol shrimp and watchman goby. The tank is 20 gallons, all the fish are light eaters and I have 20 lbs of live rock and corals.