The only thing is your Pydochromis, I have one and it rules the tank. My gobies are all in hiding so that the chromis don't kill them.
I imagine it DOES rule the tank since none of the the other fish know what it is?! :p
Just to clear the air and cover thincat's back... I'm thinking he means pseudochromis... and didn't mean "chromis" in his second sentence. I don't think a chromis could kill a knat if it wanted to.
Regarding adding stock - I don't think you're at your limit bioload-wise, but I might be a little hesitant to add anything else with two pretty feisty fish in there. 30g can get pretty small when you're a fish running for your life!