Tangs by their nature are swimmers and require the swimming room that longer tanks provide. ( 6 feet).
Thank you for showing your concern by asking before buying. In time you will have a tank to accommodate their needs and will be able to buy one at that time.
The best website for information, other than canreef, is
www.wetwebmedia.com.
There are articles about tangs and other fish coral and inverts as well.
There is also a new updated paperback by Robert Fenner "the Conscientious Aquarist which I would recommend.