All that I can add on this Quan is that in the ocean they swim long ways very quickly. So IMO they are a fish that needs to have space to get going. I think that is why WangoTango suggested the 6 foot tank and did not mention anything about how many gallons. I would agree with him on this.
I believe that ultimately your choices are yours. I myself keep a foxface in my 29 gallon biocube. This is not recommended and if there were Rabbitfish police I would be in Davey Jones Locker by now. I am on my fourth one. I buy them at about 2.5 inches and trade them in at about 3.5 inches. I keep them because I have an ongoing Caulerpa problem and they keep it mowed down. I know I am going to do this and do not deviate. I have no grand notions that I am going to upgrade down the road and move it into another tank. Is it right IDK nor do I really care about the "moral" issues involved with it. My fish are healthy, fat and in excellent shape when I turn them into the LFS for credit. They take everyone and they are sold quickly because they are healthy.
My choices are mine, your choices are yours. Again I agree with WangoTango for long term keeping of the fish you are looking at.