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

Hey all, this is not for a Mopar, so I apologize in advance.

I'm helping a neighbor replace her busted up door and fender, so we found some parts at the junkyard. Her car is red, the replacement door is light blue, and the replacement fender is white. My question is what's the process for prepping the existing parts to paint red?
20240806_083813.jpg
My uneducated guess is to sand with maybe 120, 220, or 320 grit, shoot with primer, shoot the color, then clear.

Am I on the right track? Both replacement parts are straight and require no filler -- simply a color change.

I'm also wondering how to remove this trim piece. I can't lower the window. Does it simply snap into place?
20240806_083830.jpg

If it matters, the car is a 2010 Camry. Thanks in advance.