Hard to give specific answer without study of what you are doing. You say "some rot". We don't know where and how much.
So general advice:
1. A cab is a 6 sided box. But two of the sides are mostly doors. Which are not doing too much to keep the geometry ridged. Especially when removed
. The windshield opening is not much help either.
2. Since your work is low down, you do have reasonable support depending.
3. You are going to remove the floor and associated items like rockers, cowls etc. So therein lies the danger.
4. Visualize what removing something will do. Use common sense. Sequence the events by studying the box and maintaining the box. Doing a whole one side may still cause big trouble. Big trouble is: doors won't fit when you are done. Patch panels will not fit at all..... and they don't fit perfect to begin with.
5. Sometimes bracing is need on the inside of cab. Across from hinge to hinge pillar and across from latch to latch pillar. This would be maybe half way between the dash and floor. The bracing would depend on size of cutout metal, it's location and effect on geometry release. Other bracing is done at each door opening. From hinge "A" pillar to latch "B" pillar, to maintain the opening. Bracing is not always necessary. Example: putting in a patch in the middle of the floor.
6. The general rule is only repair rust. Only cut out what is rusted. Keep good metal. Don't use the whole patch if not necessary. Sometimes you use more of the patch and cut out good metal to reach a better butt seam resting/welding place.
7. You can't use bracing that only pushes outward or clamps inward. You have to bolt or weld them because you don't know if the box will expand, contract or twist.
8. Some folks use an "X" brace instead of one, each place. This may prevent twist when things are cut/box is "released".
9. We can't be specific because of all the variables with each project.
10. Search the internet for cab weld bracing, or floor replacement or rocker replacement.............lots of pics and advice. Study study study.........then do.
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