Hi,

But even then I assume I can only get ±0.02mm flatness using hand scraping,
Hand scraping is a useful technique to go from 0.01mm to 0.001mm, but any suggestion that you can remove as much as 0.1mm is a joke....you'll be there forever. Milling or grinding to within at least 0.01mm
is the answer, scrape if you think it will add anything but don't imagine you can remove any large volume of material.

Craig