On the "how long", with 6 COATS it might take a few days before it hardens enough to buff. Try some 1500 DRY first and SEE if the residue "ball's up" under the paper. If it DOES,it's still too wet to sand.
If the 'peel is bad and having that many coats you could start with 1000 then up it to 1500. I'd say 6-800 but it's real easy to cut thru with those grits so I wouldn't go lower than the 1K.
Be SURE to keep your buffing speed under 1700 RPM. SO be carefull that you get a buffer and not a grinder.
WATCH THE EDGE'S !!!!!