Your tank size can handle the fish, but another consideration is your aquascape. If your fish have plenty of hiding spots they tend to do well, but I have found that in a minamalist aquascape that lack of hiding places adds to the stress of larger fish. I had 14 tangs in my 400 and I was having some stress issues do to minamalist aquascape. I now have 5 tangs and they are all doing very well and show much less aggresion as they do not have to fight for hiding spots.
I have a Orange Shoulder as well, one of my favorite tangs. I did not know that the Orange Shoulder is a Anacanthus Tang and in same family as Achilles until a recent read. I have never had ick problems with this fish compared to the Achilles that did not work out in my busy reef. I had a few of my tangs in a 120 before I got the 400 and I can say that the fish seem to grow faster and larger in the 400 compared to the 120.
Good luck with the move and you will be fine.