I'm pretty sure that anything you need to do to the cab corner you're going to have to pull the seat out anyhow. (and the B pillar trim, sill covers,...)
Not sure what "over time" means to you.
I'd likely deal with my 1/2 rubber mat while welding up the floors, then paint, then install insulation/sound proof and carpet at once.
Vote 4x???
Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with a Holley 80508 and Performer intake.
Too much other stuff to mention.