Nice find and welcome.
See my build thread on this forum "84 Grand Wagoneer Revival"
Good to hear you went through the fuel system already. Now...go through the engine bay, and find every bolt you can on engine, fenders, firewall, grill, and snug up all of them. Electrical connectors, unplug, clean, and plug back in. Grounds, take them off, brush up nice and bright, then reattach. Check all vacuum lines that are attached, and replace what needs replaced. Spark plug wires I would recommend replacing with a new set now, as I did not when my rig came home, and fought for months and money trying to get it started. Found after my friend and I both got zapped, the plug wires were junk, and 99% of the problem.
Tailgate issues - don't count out the existing switches just yet. Found my rear window poorly performed, and found the ground on the dash switch needed cleaned. It is right behind the switch and up above the parking brake. THIS is the ground for the tailgate window. I also rehabbed my tailgate key switch, and both switches work like new now.
Go through the tailgate motor, clean out, and get some fresh lithium grease in there.
Defroster wires are on the passenger side of rear glass, and common one will be broke. Mine was the ground, but not fixed as not needed in AZ right now, and have other wiring issues more needing fixed right now.
Same with the doors, go through and open up the motors and clean/grease, which should resolve those issues. BJs Offroad has seal kits for all the doors & glass, and most of what you need to get the rig back to good condition.
https://bjsoffroad.com/login.php
I replaced my factory mirrors as I needed larger ones for towing visibility. My OEM ones I have in a box in the garage.
AMP gauge replaced too. See my build thread, or others, as it is a common upgrade.
Oil leaks, back to my first comment, go through and snug up every bolt/screw you find. Check everything over so it is safe to drive, then start driving it. Get some miles on it slowly and close to home. As you put a few miles on it, get a feel for how it runs/drives/performs, before digging in too deep to "fix" something that might not be broken. It just needs some exercise, so everything can get used to working again, and many times you find some things will resolve by just driving it.
Issues directly related to engine or transmission, check here first through your own build thread or comment on others. If really technical, I consult on the AMC forum, which has been a ton of help with my 401 engine & 727 transmission.
https://theamcforum.com/FORUM/forums.html
'81 CJ5 Base, 258 I6, MC2100, T176 4 spd, 300 TC, D30 Front NT, 3.31, 2-Piece AMC 20 rear NT, 3.31, 4" high arc spring lift
'84 Grand Wagoneer, 401 V8 (.030 over), Edelbrock clone 1406, 727 auto, Selec-trac NP229, AMC 20 REAR - D44 FRONT - WT 3.31, 4" high arc spring lift
Rather be driving, than waiting to be modified