Can't comment on the P-40 kit Alex, as I don't know enough about the various kits. But for an airbrush, you'll find a simple, double action, gravity fed version easier to use, and also it'll allow you to cover a relatively wide area and, with practice, down to very narrow lines of at least 1mm.
I've had three, inexpensive 'brushes from the same company, which have all worked very well indeed. They should last at least three years before needing any major servicing, when, to be honest, it's as cheap to buy another one.
I've been using a small, very simple compressor for the last six years, again without problems, although I may replace it soon.
I got my stuff from the company below, who's prices are low, their service excellent, and the 'brushes are their own manufacture, now back under the 'Aerograph' name. Look under their own 'AB' range on the web site.
The Spraygun Company Ltd