when you do it, do them all at same time, i have always made sure there are odd numbers of tangs once over 5... I have had sailfin, white cheek, yellow tang, and a hippo. No problems. I have always made sure they all are interduced in close times, with in a week usually.
At the Georga aquarium the reef tank had 10 types of tangs, and probubly 200-300 total all getting along, granted it was a huge tank!