Nice job! Would have gone gold, but ya know
Its always nice when you can bring something back like that though and it probably saved you a ton over getting new wheels.
On the powdercoating question, I've never had to seal a PC part against a non-PC part but I would think you would be ok to not sand it off. The only catch would be that the PC was applied properly and is level...if it has any dips/changes in elevation I would sand it off to be safe.