Airbrush boffins. Info needed please.

Guys,
I need some basic questions answered here. I've always originally used either tins of enamel spray paint to paint kits, or the Tamiya rattle cans. I've never had any success with air brushing, but that is probably because I had cheap equipment or the wrong stuff.
Can I ask some the more seasoned spray painters (Tamar, others), what to look for, and what equipment you use\suggest?

Some questions include:

Make of airbrush, single or double action
Size of compressor, is a water trap needed
Paint reservoir on top, below brush etc?

I believe the enamel paints I've been using react with the plastic resin I'm casting with, softening the finished product. If I was going to buy a brush, what would I need to look for.

thanks in advance guys

regards

Alan