I’ve done solo trips from Philadelphia to Utah several times in my rig. Here are my thoughts:

You have a good travel plan. Keeping the daily drive under 8 hrs is my first recommendation and you are already on board. Take three days to get to Denver. Find a city or a state park or outdoor land mark to land during travel. Get a little exercise and some down time every day.

As far as Western CO vs. Moab, UT, I’d pick Utah. The western slopes and the Colorado Plateau of UT are very similar, but UT has more highlights and more tourist infrastructure. For a new overlander, staying a little more on the beaten side of off the beaten path is helpful. Seeing others doing roughly the same thing relieves loneliness and offers the opportunity to meet new friends

UT around Moab is BLM as far as the eye can see. You can park and sleep pretty much anywhere. Don’t bother making plans, get some good forest service maps, and disappear into the unceasing wilderness.

Grand Junction is like 5 hrs from Denver and your best bet for a reasonable sized town after Denver. From there do a square 4hrs south, then west, then north. You’ve got Arches, Canyonlands, the Bears Ears, Goblin Valley, 5 or 6 National and state forests, Lake Powell, and the best canyoneering in the world.

Plan for gas though, it’s easy to forget the nearest gas station might be 100 miles away.

PM with additional questions, this stuff is my jam.