Nice work, removing the tar mats. That's a nasty job, but now you know exactly what you're dealing with.
I'd suggest removing the floor plugs to get at the rust in the seams and putting them back in after painting them/the floor.
(there was some rust under the rear seat bulkhead, so I took that out).
I used a tube of auto body 'caulk' when I put the plugs back.
(the red tube)
I put it between the pieces, before twisting them into place (after I tapped the tabs back into shape, so they would pull them in tight).
I also put circles of the new sound dampener over the plugs.
The pieces of 1/8" thick wire they used to hold the insulation pads in place were rusted/weak/broken, so I ground those off and made new tabs out of sheet metal, then tack-welded those to the floor. You can also see the patch panels I hammered out/welded in where the pan was rusty. My puddle box needed patching too.