I'm about to start work on my next project. While I am well versed in panel replacement and fabrication, I've never tackled a job which requires SO much metal replacement.... I'm replacing all the floors, quarter panels, dutchman, roof skin, a-pillar work and the right inner fender- all with the idea of getting the car on a rotisserie for final paint. My question is how to best support the car after I start cutting on it, and is there a preferred order in replacing the parts? My plan is to start with the floors beginning in the front, then quarters/dutchmen, then roof with the car sitting on all fours and then gutting the car and leveling it on stands to replace the inner fender. Any suggestions on how I should proceed?

I would replace your floors 1st. And install frame connectors to kept everything solid. Before I did anything I took my car to a frame shop and had it checked for staightness. It had to be pulled in a few places even though the car looked ok. Before replacing the floors and stuff. I would try and get the car as light as possible so there is no strain of the frame, rocker panels, etc... when replacing the floor pans. Which means removing the engine and tranny, rear axle, tires etc... Place the jack stands just ahead of the leaf spring front perch on the frame and just about one foot ahead of the front crossmember just before the frame rail starts going up. Thats what I did on my 68 charger. (I left in the engine and tranny but I had the front also supported at the K- frame) I had to replace some of my cross member which I did while the floors where in. I just cut out the floor where the crossmember was bad and replaced the bad section of crossmember. That way the floor helped support the car while I was fixing the crossmember. I also supported the middle of the rocker when I was replacing the floor. I have some pictures I can post later. You may need to brace where your doors are when replacing your roof. Having frame connectors in place before doing your roof would help a lot.

I could post some pictures later of the crossmember fix.

Sounds like you have more experience than I do. I'm just telling you what I did. Hopefully someone with more experience chimes in.