Firewall Repair Questions, Am I over thinking this? Options

[amfab]

I am a little concerned about taking too much metal off the car before I put some back on. This is a question about order of repair/replacement of the firewall

In terms of support currently I have:

2 jack stands at the front end of the torsion bar tubes
2 jack stands supporting a 2x2 steel bar running under the front floor pan just behind the wheel wells
2 jack stands supporting a 2x2 steel par bolted to the 4cyl engine mounts
2 jack stands supporting the tubes that stick out from the front of the rear trailing arms
Doors braced from upper rear seatbelt holes to welded plates where the speakers would be.
The longs are open but sleeved on the bottom and side with another layer of 18 ga from the door pillar to past where the long turns upwards.

Currently, after checking for the umpteenth time, the car is level, measures to factory specs accurately and the doors are on and the gaps are good (at least as they ever were)

In terms of lack of support currently I have:

The inner rockers (outer side of the longs) removed and some metal of the long cut back behind the jack point
A hole in the top of the passenger’s long to repair in the hellhole area
The inner lower firewall removed
6x6 hole in the rear corner of the passenger’s floor pan
Rust perforations along the side edge of the floor pan rear of the cross member
A 2x2 hole in the upper passenger’s firewall where it meets the top of the long

I need to replace the upper firewall—both sides—from the center of the “X” Stamp down to the flange where it meets the lower outer firewall. The center bulge is OK. I have a solid donor firewall.

I need to replace the lower outer firewall completely. I have the RD piece

Question: Is the car supported well enough to cut further, and what should I cut first?

I am thinking to be extra safe, I should drill the spot welds connecting the lower firewall to the upper firewall and replace rusted upper firewall sections one side at a time. Leaving the lower firewall in place for lower body lateral support.

Then once the upper firewall is solid, I cut the lower firewall from the longs and replace the lower outer firewall.

Am I over thinking this? Is it supported well enough to cut it all out at once? The top of the upper firewall/Targa bar combined with the support bar across the motor mounts should keep things laterally aligned enough to do it all at once shouldn't it?

Once again, thank you all for your advice, it is invaluable.

-Andrew