another two cents adding to what has been said/written above:
Priority number one: Get a compressor with a tank and a pressure controlled switch, the compressor will shut itself off when there is enough pressure in the tank and start again when the pressure drops too low. Without a tank you can get a pulsing air flow and even a high quality air-brush can't make that problem disappear, you can get blobs of paint instead of fine lines.
Priority number two: Good quality air-brush, ask around, Badger has been mentioned (double action) and they will do nicely until you have learned a lot and want something more advanced.
Priority number three: A silent compressor. The noisy ones make a lot of noise and this will get irritating in the long run (unless you can hide it in the garage or something), think really noisy vacuum cleaner and then double it. The silent ones make about as much noise as a refrigerator.
A large tank will compensate for the noise, run the motor to fill the tank and then shut it off and enjoy almost complete silence, if the motor starts suddenly right by your side it may scare you into dropping your model on the floor

/ Robin