Things I forgot:

I'd probably go with a short travel fork. With a load, even in a trailer, the bike will handle differently. Trailers tend to make the bike tail heavy and a long travel fork will raise the front end making it even lighter. You want a fork that will take the edge off but you don't need something for big hits. It's not that rough a trail from the parts that I've seen here in Colorado. I would also get a fork with a lockout even though it adds complexity since there's still a lot of pavement on the route.

Controls: I gather from another post that you are familiar with touring already so I don't have to harp too much on comfort of the controls. However, mountain bike bars are very different from road bars. You don't have as many hand positions which means that you put a lot of time in with your hands in one spot. Also, you don't want a set of bars that is way lower than your saddle but you also don't want to be sitting bolt upright either. First, when you install the fork (use threadless since it's easier to adjust) cut the steerer longer than you otherwise might. You can always add spacers above the stem. I'd use a 15 degree stem and riser bars. I'd also put bar ends on the riser bars. You won't need them for climbing necessarily but for the added hand positions. You might even want to look at a trekking bar but I, personally, don't really like those.

For grips, stay away from anything that is too firm. I did a solo trip on a mountain bike long ago with solid rubber grips and it took 6 weeks for me to get the feeling back in my hands. It's not a pleasant experience! I'd suggest something like Grab ons. Look at the leisure grips or one of the softer grips on that page. Grab ons have good grip when they are wet (something that will happen) and they have a bit more cushion than most of the firmer grips out there.

Finally, saddle. A shock post might be a good idea although it adds more complexity. You might want to consider something like a Brooks B67, the Champion Flyer or the Conquest instead. Or you can go with a regular plastic saddle. Whatever you get make sure that it is comfortable for you and that you put a lot of time in on it before you go. But you already know that