I am also about to start airbrushing. I have been looking around mainly youtube and this website but from some research what i have found best ( not from experiance) is dual action, external mix, gravity fed, and .35 tip size due to being able to do fine lines.
Im on a big time budget due to a baby on the way but i went ahead and bought the Iwata eclipse ( gravity fed) from hobby lobby using the 40% off coupon for a decent price i think. I think i paid about $130 for it. Hope this helped alittle bit, its my first post.