Serious Sheet Metal Opinions

Need a little guidance from some who have "been there, done that". I have removed the entire floorpan from the dart. I welded supports in both doors and crossbraced in the rear seat area. Jackstands just ahead of trans X-member and frame under rear seat area. No glass, drivetrain, front or rear suspension. Haven't detected any flex so far. I'm going to weld in the new pan and then install frame connectors and form side plates from the frame to the new pan. At that point I need to know which direction to go. I have a full trunk floor, side xtensions and full 1/4 panels. In what order do I replace the sheet metal? Floor first? 1/4's first? Should I avoid the rotissire until all the metal is in to avoid flex issues? Do I need to brace for the trunk/xtensions/quarters? I'd rather overkill than fold my car up. Any experience out there?