Own an '04 (~ 300k) and a 2012 (208k). Gonna need DYI maintenance advice.

Howdy. Most honored to be here.
I'm not an off-roader. I've got a dirt bike for that. Occasionally I cruise well-traveled, predictable jeep trails (though we really need to start calling them Toyota trails) like Engineer Pass in SW Colorado. But mostly my Tacomas just get me & my kinfolk to work, to ski areas and to dirt-road accessible camp sites.
I joined because I've got over a half million miles, combined, on both rides, so I'm going to need maintenance advice.
Words can't explain my gratitude at having had so few maintenance issues with either vehicle. But entropy is real, and nothing lasts forever. Something is bound to go wrong and I'm gonna need advice. I've gotten spoiled by never having to do any serious maintenance. My goal is to keep each of my Tacos running past a half-million miles.
It wouldn't kill me to sign up for an entry-level community-college auto-maintenance course. Unfortunately I live/work in the middle of nowhere and that's not an option. I would be very grateful for recommendations of books, online courses, youtube videos and the like, targeted at someone who is able to change his own oil ... but can't figure out which 2012 under-seat electronics to disconnect, before he removes a seat for carpet shampooing.
A pleasure to be here!