I had one for a few months but I ended up rehoming him. When I first got him he was very healthy and didn't have any ich on him at all. Unfortunately after 2 days of being in my tank he got completely covered in ich
None of my other fish had any ich on them at the time I got him, but I knew my regal tang would get a few (2-4) ich spots every now and then (about every 3-4 months). The ich would last about 2-3 days and the regal tang would be ich free for awhile again.
Unfortunately the proc puffer I had stayed covered in ich the whole time I had him. After I few months I felt bad for him and I ended up giving him to a friend of mine, who luckily was able to keep him ich free in his tank.
As far as I know proc puffers will leave all types of corals alone but they will eat snails, and possibly crabs and shrimp and small fish. Your clowns would be fair game.
If you're wanting a puffer I would suggest a toby puffer. I love my little blue spot toby puffer and the two things I was most worried about (when deciding whether or not to get him) turned out I need not worry about. #1 He never got ich and #2 He hasn't nipped at anyone. At the store he came from he picked on/nipped at the frog fish but he's well behaved in my tank. It's probably because he's with large semi to very aggressive fish, but with the fish you have a toby puffer would most likely behave himself.