Hello, - you asked about airbrushing...
I just started with a Testors MightyMini that I got on the cheap at a second-hand store. So here's the little advice that I'd give, based on my humble experience.
-Don't waste money on a little airbrush compressor. Get a bigger one from a hardware store, as well as a moisture trap. You can also use it for blowing dust off of parts, and out of computers. Some of them come packaged with an air nailer/stapler. (I'm pondering getting a Sears Craftsman compressor myself.)
-I do like the simplicity of the Testors airbrush tips. They come apart with only a couple parts, and clean easily, making color changes a bit faster. - with an internal mix badger you practically have to take apart the brush for cleaning, or use a cleaning station to run the paint out of it.
-dual action sounds cool to me, but they cost more, and probably take more time to master (Paul-any comments?) - the single actions work just as well.
with my cheap single action, external mix brush, i've done these re-paintings of plastic toy guns:
http://i40.photobucket.com/albums/e2...gunrepaint.jpg
http://i40.photobucket.com/albums/e2...terrepaint.jpg
I still have yet to figure out how to do flames.