Lionel also made a hanger kit. Both Lionel and MTH made control towers that can be used as well as radar towers and rotary beacons. Lionel has made the Red baron, WWll, and other towers with circling airplanes. There are both plastic and balsa airplane models available in 1:48 scale. Plus there have been die cast airplanes by various manufacturers.
Runways can be made from painted wood boards with holes drilled for mini **** lights. To save room, you can paint the runways on the backdrop. There are several figure sets that can be used for mechanics, piolets, military etc.. Hot air ballons, and air ships are available on ebay. K-Line also made a rotary beacon and I believe Ready Made Toys by AristoCraft has them now.
Lionel has Cesna planes on a flatcar and other space/military cars and accessories.
ChessieFan72 had a great list of factors to consider.
Paul Goodness