Hi HB,
I already do this, also custom mounts.
There are a couple of examples on my website, Old Scottish Shed and Tranquillity. I also painted the picture of the shed with the air brush, only my second attempt ever at any form of painting.
Do a search for this guy, Michael Cacy, he has some excellent articles on the net.There are also a number of websites with good information.
I use "Golden Artist" airbrush acrylic colours, they mix well and spray straight from the bottle. I use thinned acrylic gesso as a basecoat,and finish coats are thinned artists acrylic varnish.
I was lucky I found a complete professional setup (gun compressor etc) on ebay as new, and half the price.
Best advice I can give is keep away from the cheap end of the range,the top end are difficult enough to master, bottom end almost impossible.
Feel free to email me if I can help further, I am also on MSN messanger, username/ID:
mick@pictureframing-uk.com
HTH