First off, do some research into how airbrushes operate and what the differences are, say between single action and double action. If you don't know I'd be happy to elaborate.
Once you have finished with that, you need to sit down and decide what you will be using it for and how much you will be using it. Then comes money; how much are you willing to spend? And don't forget to figure in an air source. Again, I would be happy to elaborate on any, or all, of these points.
Personally, I like Iwata. I've been using an Eclipse HP-CS paired to their Smart Jet Pro compressor for many years now and it performs flawlessly, though you pay for it. The airbrush itself was only around $100, which is pretty good. The air supply is where it gets you, the Smart Jet Pro was around $300. I'd do business with dixieart.com, their prices are good and they are very professional.
As far as the primer goes, you have a couple choices. To me the "luxury model", so to speak, is Tamiya's Fine Surface Primer (I prefer gray since it doesn't hide imperfections like white does). I spray it straight out of the can, though you can decant it if you prefer. A cheaper alternative that is still good is Duplicolor Auto Primer (gray), which you can find at Autozone, or places like that. It doesn't adhere quite as good as the Tamiya stuff, but it's more than adequate. Gunze Sangyo makes an excellent putty/primer mix called Mr. Surfacer that comes in different consistencies (500 thick, 1000 ~normal, 1200 super thin). You can get it in aerosol cans or in the bottle. It's a little tricky to airbrush as it needs to be mixed with Mr. Retarder to lengthen the dry time. I find it very useful to hand brush onto kits and then sand to fill in surface imperfections. These are all just things to keep in mind. I won't take up anymore of the page, just let me know if you would like me to elaborate on anything mentioned here, or have any further questions.