If it were me, I would wait a bit til water tests prove consistent, algae is under control and a few weeks have past by. I like to keep fish in my tank that I know will live in my tank for their life time. Granted, I tend to push the envelope of stocking my tank, but not to the point of effective water quality.
I can't tell how large your fish are, but their potential are pretty darn big. Are you planning a larger system in the realistic near future? ( I ask realisitc near future cuz we all have plans for killer 500 gallon beasts that may take a while to build). If so, you could keep what you have if you plan to move them in under a year.
If not, plan for no more than a total of 20 inches of fish - at their maximum length (even that is pushing it for a 75). The longer your tank has been established, the more you can push the stocking limit - to a point.
I saw three tangs, which alone will kill your stocking limit.
Sailfin - 15 inches in the wild, realisitc - a foot in your tank
Regal blue - 13 inches in the wild, realisitc - 10 inches in your tank
Yellow tang - 10 inches in the wild, realistic - 8 inches in your tank
There is a huge difference in contaminates to your tank the bigger your fish get. For example. 8 one inch fish are much cleaner than 1 eight inch fish. So, it may be best to keep one tang and have a series of smaller (say 4 inch) fish to compliment temperment.
You could keep the Yellow tang, add a pair of clowns (unless you already have them), toss in a flame angel (man I love those) and keep your three stripped damsels, for instance.
Your tank, up to you.
-Dr Marco :sfish: