We've done some of the national parks in Utah in early October, and it was perfect weather. We hit Zion, Bryce, and Grand Staircase-Escalante. We flew into Vegas, which was relatively cheap.

I did Grand Teton / Yellowstone in mid Sept and it was magical. So quiet and tons of animals. But it was already cold with occasional flurries (no serious ice or snow driving).

I’m not sure you’d need / want 5 days though.

I wouldn't recommend Orlando in September. Rainy, hot, and possibly hurricane season. But November is perfect for Universal Studios FL. If you are ok with him missing school, it's less crowded and usually good temp and drier.