The basics of creating aircraft textures / skins for Falcon 4.0
Only use 1 texture per aircraft. Spread out the UV mapping covering as much of the texture space as you can.
Do not create 2048 x 2048 resolution textures, they are just too large. Usual textures should not exceed 512 x 512 resolution, you can use even 128 x 128 for secondary aircraft's. The highest res is 1024 x 1024 for example F-16 models or other “popular” jets.
Use DXT-1 texture format when saving.
Save textures using mipmaps.
It has been said that if you are experienced texture painter and are working on very popular jet like F-16 which people love to fly, you CAN indeed use 2 x 1024 resolution textures, but not more than that (and you still should try very hard to use only one). Also make sure you efficiently use the texture space in those textures.