Just getting back into modeling and want to do things right, purchased a testors mini blue compressor with an aztec a220 single action air brush, is it worthwhile to upgrade to an airtank and/or pressure regulator? high end units are $450.00 certainly do not want to put out that much money, or would a double action brush be sufficient? flow is adjustable on double actions right?

David,

Attach a pressure regulator to your copressor air line, one that has a moisture trap attached, as most airbrushes work best at between 10 - 15 psi the regulator will control the air flow too your airbrush only.
With a double action the paint flow is controlled by, retracting the trigger, the airflow is the same regardless of what airbrush is used.

Hope this helps.

sounds good, will buy the regulator and give it a try, should be good for most painting I assume and probably upgrade to a double action brush down the road.