If you're 3 years out, my advice would be to table your search until you're 6 months out. Nothing you research today is going to be relevant in 3 years. You're just staying busy.
Where it stands today, cellular signals can be hard to come by on BLM land. I have a weBoost that helps increase my signal strength but no signal at all means no cellular service.
Right now, Verizon seems to be the best carrier for nationwide service but may not be the best for the specific area you plan to be in. I have Verizon's unlimited plan, and go over my max data every month. I've never had an issue watching videos or "TV" on my tablet. Just because you're throttled doesn't mean your phone stupid working. If you're not using heavy data, like someone who's gaming, you probably won't notice it.
Cellular companies come out with new data plans all the time, and there are new companies offering services all the time, so again, unless you just like doing the research, I would wait until you're a lot closer to heading out before deciding which company to go with. If I were you, my focus right now would be on camping out in my car to see if I liked it.