You will want down to at least 2000 grit. Trust me, I worked in a car bodyshop for a summer when I was a student....

It is a big risk. But if you are determined to risk it (and you run the risk of turning a $50 job for a pro into a $500 job for a pro) then...

Try this first:

If the scratches are not through the existing finish, try polishing with brasso or non-chemical silver polish, and you may get most of the roughening to disappear.