stocking a 5.5 gallon

[jba6511]

I have a 5.5 gallon with a yellow rose antenna goby/tiger pistol shrimp combo. I am wondering if I can add any other inverts, such as a procelain crab, boxing crab, etc. I just want to get a general idea if I can even add anything and what everyone would suggest. I am going to add a turbo snail and a few corals, mostly softies sometime this weekend.