Travel trailer questions from an RV newbie

I would suggest a travel trailer approx 20' long. Pick a floorplan you like, that is likely more important than brand. For a long trip such as you plan, I would buy a used 3/4 ton, crew cab( four door) truck, with a gas engine. I'd put a cab high cap on the back. Budget 10 mpg or slightly less, because that's what you're going to get, no matter the length or weigh of the trailer, or for that matter, no matter the tow vehicle for the most part.
Enjoy. It will be an awesome experience I'm sure.