In the long run that puffer will need a bigger tank. Also when the huma, and yellow tang, reach adult sixe the 2 alone will be crowded in that size tank. Having 2 tangs in a 75 is not a good idea anyways.
also watch the huma huma as it gets older it can start going after the porky I had to got rid of mine for that reason about killed my porky.
just a heads up.
Mike
That sounds like lots of big fish in a little tank. Remember that a Naso can get up to 16 inches, even in a smaller tank. THAT IS A BIG FISH. I think you should unload a bit, and perhaps get some smaller fish.