You’re quite right that you can never go to a finer grit on a used lap. However, you don’t need 7 sizes of diamond. The 0.25 micron is probably a good polishing grade, and the 5 micron, is about right for most prepolish. I stopped using pastes and powder when Gearloose came out with the Diastiks, and now use the newer Pandimonium. For suggestions, take a look at https://gearloose.co/product-charts/