PTs are wonderful fish, I have three. They're tough to find, like all Red Sea fish now, because of all the tension in the Middle East. IMO & IME, IF they have enough room they are easy fish to keep. If you QT your fish, ich isn't a problem, its very easy to cure in QT. If not, I wouldn't get one. But, I wouldn't get any fish without QT. Its too bad that your fear of ich determines what fish you can get. There are lots of other deadly parasites, diseases, etc, that can enter our tanks. Ich is only one. Again, QT is the answer.
BTW; its impossible to give any real opinion without knowing your tank size. If your profile is correct, and you have a 75, IMO that is too small for any of the tangs you're talking about and adding another would be a big mistake.