1. I look at the color of the walls, or the color of the wall lights. You usually spawn in your "area". Either that, or you can do a quick melee, and look at the color of your arm.

2. I never paid attention to the names, but the enemies on the radar are red.
3. The enemies on the radar are red, but the uniform colors are static (blue are "blue team" etc.)
4. This I don't know, but I'd like to. Especially if there are any weapon benefits that come with increased rank or experience. I haven't checked this out yet.