Well, I follow a certain order when painting planes. If they are all one color, then yes, you can paint it all at once. If it's a bi-color scheme, I paint the underside color first and let fully dry. Then, I paint the topside color or colors starting with the lightest color first and the darkest color last. You have to let the paint fully dry in order to apply all the colors if you will mask. If you use acrylics, I would let dry for 24 hours. If you use enamels, I would wait for 48 to 72 hours. Now, if you are going to airbrush freehand all the colors and use no masking, then yes, you could paint everything at once. Just allow a small dry time between all the colors. Hope this helps...
Andy