How should I prep for a color change over existing good paint?

I do have one of the purple guns, a Bostitch, and a Nieko. I don't remember the tip sizes of the other two.

One of her coworkers painted her bumper a while back, but it looks pretty rough. Maybe I'll test out my skills and redo her bumper while I'm at it. If I do that, would it make sense to just shoot clear over the entire car?

She must be pretty hot!