First, don't skimp on the truck. I would go with a 150/1500 truck set up for towing. Depending on the specs you can pull over 10K pounds. Having some excess capacity is great for longevity, for safety and you will be really happy to have more power towing in mountain country.
I cannot help with the trailer size or brands since my wife and I full timed in a truck camper, not a trailer. I can make a few general recommendations. Be sure the trailer has good tires and suspension. Many are poorly made and just not up to what is needed. Modifications and accessories can add a lot of weight. Personal gear including food can quickly add another 1000#.
I highly recommend a cassette toilet. They use minimal water and you can dump in outhouses or other places when dump stations are not available. You will also want to save weight and space with a wet bath. One minute with a squeegee will do a remarkable job of drying the area.
Look for a unit with relatively large fresh water capacity. I have learned to take a shower with 1 gallon and get by for everything else with another 2 gallons a day. You will want an absolute minimum of 15-20 gallons of fresh water. Next look at battery capacity and solar. You cannot have too much and a minimum for me would be a couple of batteries and a couple of panels.