You should stay away from the Damsels. They are beautiful fish but they are aggresive.
green chromis are ok to have but I would put any other damsel fish in there. Fish at the pet store do well because of the great filtration they have and the amount of water all those tanks share. They can get away with ovrstocking because there are usually far too many aggressive fish placed in the same tank that they actually get along for the short time they are there. Some tanks dont offer hiding places to more aggressive fish in crowded tanks so no one can try to defend a territory. Anyway...I wanted a dottyback to but I chose the Royal Gramma which is a beautiful fish and my ocellaris clowns and her get along so well together. They swim with her like she is one of them. It's adorable. The yellow watchman goby is beautiful and peaceful but I have heard it is harder to keep. It also has been reported to jump so make sure you keep a lid on the tank.
Do you have
live rock in your tank? Is this a Nano (just trying to figure out equipment). how old is the tank and what is the parameters right now? Personally, I think the two ocellaris are about the only thing I would keep in a 30 gallon. I have a 55 gallon and I have two ocellaris, one royal gramma, and a firefish which is new in my hospital tank. Do you have a hospital tank?