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

Thanks everyone, lots of helpful advice.

The damaged fender is already removed, so I'll take it in for a paint match. She already has some paint leftover from when someone else painted her bumper, but it won't be enough for the door, fender, and blending. The paint is metallic, but I don't know if it's 2 or 3 stage -- I'm a complete novice when it comes to paint & body work.

So, I'll sand the damaged panel to get the correct color of the sealer. Wet sand the replacements with 600, epoxy primer, sealer. Paint the jambs and inside of the fender off the car, hang them on the car, then paint & blend as necessary. Does that sound about right?

And a quick search says I can buy a replacement belt moulding fairly cheaply.