what to do first and then what else plus some questions

That's a normal amount of buildup to see on a magnetic diff plug, there's no filter in there so the magnet is there to trap the wear metals.

 

My magnet looked about the same.
Wipe it off and stick it back in. You are good

 

Mother f@#$er, I'm blown away by those plugs. They have to be original. And this thing ran good. DANG.
I'd put them in the Smithsonian for all to see.
Ohh yeah, welcome. TW will become ur new best fried, looks like it already has.
By the way, with todays market, and those miles and year, how much did u pay for the truck.

 

Hey @Jws13 , sign up here:
https://www.toyota.com/owners

Toyota used to offer a VIN checker that would tell you how it shipped from the factory, where it went and date of first being in service. I think the checker might now be available after signing up.

This site will also tell you the Toyota service history including any recall work.

Good luck