You have 8 fish in a 70 gallon tank. Most are going to say that you are at your stocking limit. Do you have a skimmer?
Tangs need long tank length for swimming to keep them stress and disease free. You are right that the bristletooth would be your best bet tang wise, but, in my opinion, a dwarf angel would be an even better option. Check out the flame angel. More exciting than a tang, no annoying algae sheets, and, they aren't ich magnets like a tang. Just my opinion :)