[Franks 72]

I to had reservations about welding . I bought a small Lincoln and did LOTs of practice welds. I have been around welding and know what a good bead should look like but never had the nerve to tackle my project (Dads 1972 4x4 suburban). The areas you show are common for rust collection. The kick panels and floor pans front door pillars (lower portion) are reproduced by many vendors and make restoration much easier. A helpfull hint is always cut in straight lines, which makes the matching of the patch (with as little gap as possible ) easier.To repair my floor area just under the kick plate, I used a piece of floor patch.
I removed the sill, but it may be possible to fix without removal. Use light cardboard ( Cereal box) and make a test patch from it
There are lots of helpfull hints on this forum and many folks willing to provide solid advice.
For the record, my floor was Ziebarted then oil sprayed by Dad for 43 years. There was a thick layer of oil / dust which I removed with a hot air gun and putty knife. It came out like it left the factory. I wouldnt put any liner or heavy material on it which may trap moisture. I had severe rust in the large crossmember which forms the transition from steel floor to plywood. I attribute this to trapped moisture in the small space between the plywood and steel crossmember. The plywood was fine but the metal crossmember was paper thin in areas.

Good luck with your project !