The like to swim fast with lot's of current and he is always on the move even at night so he will need all the space you can give him (200 + gal) on 6 ft long tank will me my recommendation. Note that it is temperamental and usually acts like the ming of the whole aquarium and will try to reign over any other tang in the tank regardless of species.
When healthy they are relatively easy to keep but is very prone to ich infestations.
O dam I was thinking they only needed like a 125 or something maybe. Seems like a lot of the tang species are easily prone to ich. I was thinking of starting a large fish only tank. Possibly with only the achilles tang in it.
How long does it take them to grow to full maturity?
I don't got the money for anything that large nor the time hahah.
I have been putting a lot of work into my 29 thought and money and it's really been paying off. I only have a few more things I want for it and other than that I just need time for everything to grow. I got about 40 corals in it now.