I plane and shape it with chisels. Very little sanding especially with a machine as it heats up quick. You can use perspex as a former and you get close to a mirror finish.
I assume you're talking about Repaircare (mirror finish). I was thinking about my experiences with regular two part epoxy. I've never tried using a chisel (or a plane) on that, always gone straight in with the sander.
Dust extractor was one of the best investments I’ve made for jobs like this. Epoxy dust is a bastard.