George...
Don't need an airbrush for this situation. Rattle cans are A-OK. In fact Art Fahey (Bar Mills) got me hooked on the use of Walmart's cheap blue-label rattle can spray paints. Their primer (gray) would be your first step. Less than $2, I believe, per can.
BUT...first get yourself an inexpensive pistol-style hair dryer. (I keep mine 'holstered' on the side of my spray booth!). The purpose of this is to follow each light coat of the spray paint IMMEDIATELY with a fast dry using the hair dryer. This will help ensure minimal/no warpage of wood surfaces. Been using this technique for years...nary a problem to date.
In addition to primer gray, I've found the same brand of flat black, flat white rattle cans to be mainstays in my shop. In fact, I, too, have built the Finley house, and followed the primer coat with a couple light coats of the flat white for the basic exterior siding color.
So, FWIW....
KD
P.S....
Two more thoughts...
LOTS of ventilation when using rattle cans....i.e., outdoors or garage preferable, in the absence of a vented booth.
An inexpensive lazy susan device (check Walmart, again) helps to maneuver the building for spraying/drying.
