Start with the cowl seam, right by the windshield. Seal it up so it doesn't get worse there. Clean the inside of the door, and make certain that the doors drain freely. Install fresh weatherstrip in places that need it.
I'd care only about the rear body mounts (aka 'rear sil') - the truck needs to be solid from a structural standpoint. Original hardware for the spare tire carrier, doors, could be swapped for new hardware.
I'd clean it-up, soap, body-wax, and corrosion-inhibiting-oil. Paint the parts that need painting. Let someone else make a showroom truck, bling, candy-paint, leather interiors, etc. Keep it rugged and kind to the owner. Toyota didn't grind their body welds at the rear sil, but, typically, every restoration uses a sander and body filler, hiding factory spot welds, turning a pragmatic machine into a sculpture, as it is remanufactured / restored with different processes, materials, technologies. Keep it in the sprit of the original truck is my incination. However, I like what
@Roastchestnuts did with his 40, as an example of spliced-in rust repairs; a sensible approach to body repairs in my mind.