First fish

Honestly for your "test fish" as I like to call them, I'd get chromis. They're cheap, usually 4-6 dollars at the LFS. Throw 2 or 3 of them in there to help get the tank cycled and make sure its okay, then you can add the clowns once your assured the tanks fine. And I've never encountered a problem with clowns taking over a tank, even smaller ones as a nano.

 

A royal gramma is pretty hearty and would get along with a clown.

 

imo if your tank is properly cycled there would be no problem adding to young clowns to the tank as your first fish. as for the clowns taking over the tank if they are tomatoes, maroons, clarkis i could see it but for percs or Ocellaris they would be fine.

 

Clowns are pretty hardy, so they will be fine.

They are usually territorial to other clownfish. You should be ok to add a pair of them first, and then other small fish later.

Maroons are going to be your meanest fish, so if you are worried, stay away from them.

 

I know in my tank i took the advice of everyone on putting in the chromis and i hated those fish so much. When i bought the clown fish i wanted they ended up killng one of the clowns so the other clown went back to the store so i could get more and they wouldnt take the chromis so they went goodbye. If your tank is cycled and you dont want the chromis then go with your clown fish that you want.