I have kept tangs for many years.
First let`s get rid of the tangs you cannot have.
The vlamingi grows very large extremely quickly . I have a vlamingi in a tank twice your size and it is going to the public aquarium soon. It needs 600 gallons plus IME.
The powder blue is almost impossible to keep even by experts. Some people do have success but IMO over 95 percent die within a year and take a few of their inhabitants with them. If you want problems get a powder blue. If they survive they are a mean aggressive fish.
The Naso grows large and is also difficult to keep unless you choose the perfect specimen IME.
A fish less than 3 inches or an adult sized fish should not even be considered as the former waste away over time and the latter very often refuse to eat. You must also see them eating aggressively. For these reasons never buy this fish online. This statement is almost true for tangs period.
I would chose a maximum of two tangs from the remainder. If one of them is a purple add it and the other tang at the same time otherwise smallest to largest.
Missing off your list is the powder brown (japonica only). It has orange on it. It is a beautiful and hardy fish but should not be purchased online.
The two tangs you choose should be plump, agressively eating, alert, clear eyes, no spots or tears. If not pass on the fish there will always be another.
Feed only garlic extract soaked food for 30 days as an ich preventative as all tangs are ich magnets.
The best source of info on tangs is
www.wetwebmedia.com/tangs,.htm