I have a hippo, sailfin, and yellow in a 175. They were all introduced at the same time when they were medium size. they have done well. In another
tank..a 156..I have a yellow, scopis and achilles that also do well. Scopis and
yellow disagreed at first, but now coexist. The achilles was added later with no problem.
From what I have experienced and read, in a well established 175 tank you should do Ok with 3-4 tangs. As mentioned by others it is best to introduce at similar times and best to have dissimilar body types.
Tangs can be ICH 'magnets' so isolate everything...even consider hyposaline everything to avoid problems.....