1500 or so is probably as high as you need to go up to before an aggressive polish. Aluminum is a soft metal, and stripping the anodizing removes the harder more scratch resistant coating. You might be able to achieve a showroom mirror finish with higher grits, but if it's going to be actually used and the maintenance is just buffing with more metal polish, I don't think the 3000 is going to appreciably improve the result unless you plan on doing that prep work every time you get a slight scuff.