Thanks for all the help so far. My questions are becoming more and more specific, and so I thought I'd clarify myself with a new OP since the other thread was getting very confusing between what I was currently asking, and what I had already asked.
Here's where I'm at so far:
#1. The bike HAS to be a steel frame. Even if other materials could, perhaps, fill the niche, Steel is just the safe bet.
#2. I need to use 26" wheels so I can replace them if necessary.
I have taken a look at the Surly Troll and the Silkroad, and decided both were overkill for my UL Touring ideal. My body, gear, food, and water comes in at less than 200lbs. When you have to lift the bike onto your shoulders and hike a few miles, 5-10lbs makes a big difference, and the right frame will be just as reliable with less weight.
Salsa looks like a great bet. In a couple of days, I'll be calling them to see about an El Mariachi-style frame with a 26" wheelset. My LBS is also a Salsa dealer, which is very convenient for me.
Here's what I still need help understanding, if anyone has some experience. This is the only question I've got left: Buying wheels: do they need to be handbuilt? What types of wheels are specifically designed for bikepacking and what are they made of?
Thanks again for all the help. Please PM me if you have anything to suggest on safety, routes, or anything else in regards to the trip. Since I have lots of time, I haven't yet begun my research on the area beyond expected terrain, so it has no place in this particular thread.