Stocking a 250 gallon tank?

You are already have a fair number of fish and have room for 6-7 more medium sized fish. Of what you are interested in I would get the Yelllow Tang and one of the other Tangs. (These get 16 inches, if you get the Yellow and both others you will be overcrowded) , the Flame Angel, the O clown, the Lionfish, the Dwarf Lionfish and the Flame Hawkfish. Puffers will be nothing but trouble, They are cute and smart and nip everything, including fingers. You will then have too little room for any more. Too many big tangs make for problems.