We always did the jambs, trunk, engine compartment first then taped them off to do the body - that way any tape lines were in the jambs and not on the body. As to wet-sanding the base coat - is your paint metallic? If so; any more than a LIGHT scuff with scotchbrite or 1000 grit paper to remove the overspray before the clearcoat can leave a brushed or grainy appearance in the finished product.