Hi,
I have never tried that combination of fish before, but you may be able to get the sailfin and the yellow or blue together in the 75. However, I would not mix the blue and the yellow.
You could split the three between your two show tanks.
However, as for q-tank, you will need more than one tank or no q at all.
I would be careful with that many damsels. What are you planning to do with them?
As for the size attained by the sailfin, I do not think it will be a problem for a 75g tank.
The size and growth rate of this fish in captivity will never be the same as in the wild. I respect Scott Michael but he sometimes overstates tank size requirement, mostly because he is thinking about community reef tanks. So, it will depend on what you have. Yellow tail damsels, specially 6 of them, does not sound that great of a tank budy for this fish.
I would also introduce the sailfin first. It is a shy fish as tangs are concerned, althought once it gets the "this is my tank" feeling he can become obnoxious. I think the yellow tang is more of a bully than this fish. IME