Hi Swanie, welcome to AH.
1. yes, only on your squad's planes.
2. your CO needs to upload it. The instructions are on this website, and are very simple.
3. Yes, each squad has unique art, and everyone else can see it (you have to get pretty close, though)
If you've ever been in the Main Arena online even once, then all of the other squads' nose art has been downloaded into a folder on your computer named Squads, inside your HTC folder. Each one of these files is a BMP, and each one is named for the CO of each squad (you'll see a file named "Dux" in there)
Maybe someday there'll be a way to put aircraft names and custom skins on our planes, but until then, the nose art does a nice job of adding a little uniqueness. It looks nice when flying formation with your squaddies.
I hope this helps.