I model almost exclusively in 1/72 aircraft, and believe me, there are some pretty tight areas on those models (wheel wells, etc.).
Everyone above has made very valid comments and I would emphasize plasticmod's comments regarding better results from spraying the smaller scales. Just the thickness of the paint alone will stand out more on a smaller model. I have been quite surprised at how little paint it actually takes to cover an entire airplane, and at how much detail remains after multiple coats (two or three color camo), especially over panel lines. I love the way you can go back and touch up tiny areas, too (I use an Eclipse).
I, for one, will never attempt to brush paint an entire aircraft now that I have been using an airbrush, and this includes tiny parts such as landing gear legs, cockpit seats, joysticks, etc. The ONLY time I will use a brush is for cockpit details (switches, levers, headrests) or for LG details like silver and black on the struts.
Get a good double action a/b, learn to use it, and you will never regret it.
As for primer, I only prime areas that have been filled or sanded, but I do make sure that my model is completely clean before painting.
Good luck and keep us informed.