Questions About Tubbing & Panel Replacement

[70LS6TransAM]

Okay, here's the deal.

I have A LOT of rear body section and panel replacement ahead of me - trunk pan, tail light panel, lower valance, left 1/4 panel sections or replacement. I'm planning on tubbing the rear wheel wells to fit 335's, so my questions are:

1) What are the differences between a) splitting the stock wheel wells and welding a strip of metal to fill in the gap vs. b) installing the DSE Deep Tub kit vs. c) installing "generic" aftermarket wheel tubs? Is trying to keep the "stock" look the main reason for going with the DSE kit or splitting the stock wheel wells? I'm not too concerned with keeping the rear seats or the stock-looking appearance.

2) Is moving the leaf springs inward and notching the frame rails a given when doing this?

3) Since there will be significant amount of sheet metal removal, what would be the best plan of attack so the entire rear end doesn't collapse while I'm working on it?
Should I leave the old trunk pan in while possibly needing to take off the 1/4, working from the inside out, doing the tubs first and working my way out, etc? It looks like the left trunk pan extension and left outer wheel well will need to be replaced as well.

I know this subject may be redundant and there are probably a ton of theads, but not specific for my situation.

Here's a photo of my current "progress"; I just don't want to get too far into it without having a plan of attack. This is my first project, so the more detailed the advice the better.

Thanks for the help!