I had nearly the same problem.
I cut out the rust sections and replaced sections.
The things I learned:
Cut straight lines, measure measure, mark or tape, whatever.
Cut straight lines.
Replace with new 10 gauge sheet steel
It should match the sections removed.
I bought a 4 foot by 10 foot 10g sheet of steel for about $110.
When you start removing the flooring, you will find support beams near the drivers area welded to the floor. If you work on the rest of the floor there are cross beams supporting the floor that are welded.
I had to replace the drivers section, very rear section of flooring and an entire wheel well this weekend.
You can do it.