- Weapon: Null-Ray Rifle
I'm a relative beginner to airbrushing myself, but I think some of my input here can be useful here.
I suggest getting a relatively simple AB and compressor set--since you're only painting TF's, there's rarely a need for complex AB-ing skills like post/pre-shading, filtering and weathering. Such effects can be replicated using pastels and...wait for it...women's eye shadow (that stuff they shade their eyelids with)! But if, like me, you're too embarrassed to buy these things at the counter, you can always get Tamiya's weathering kits.
I'm using a Tamiya Spraywork Basic AB set, which comes with a single action airbrush. The AB is actually pretty good--it functions somewhat like an double action AB in that the trigger controls the amount of paint, although a constant stream of compressed air sprays out from the nozzle.
NOTE: You'll need to buy some rechargeable six-pack batteries to power the thing, which Tamiya also sells. Failing that, you can use a power adapter. Fricking Tamiya doesn't adjust the voltage for its spray booths and compressors when exporting them, so you'll have to get adapters so use them.
With a bit of practice, you should be able to spray superbly even coats of paint.
Did you consider using spray cans? While AB's give a much finer spray and therefore smoother coat of paint, spray cans are much more convenient and maintenance free. You do tend to get more overspray from cans. But unless you're using expensive canned sprays like Tamiya and Gunze, the average industrial spray can should hold more than enough paint to complete your repaint/custom.
That said, you can easily blend and mix your own colors with AB's, which you obviously can't do with canned spray.
Hope this helps.