Body prepping a painted shell

I have a rust free shell from an abandoned project that's been painted (10+ years ago) metallic and has lacquer on top. Really don't like the colour and it's quite flat so going to repaint it.

What's the recommendations for grades of paper pre-primer?

In theory 90% could just need keying as there's only one bit of filler needed, but would I need some sort of barrier coat over the lacquer to stop it reacting with the primer?

Thanks,
Steve