Very ambitious plan you have there!
I'm not a "smell the roses" type guy, and it gets me fired up when folks here advocate only traveling for an hour or two a day max - I guess i'm jealous they have the time and money to move that slowly :)
That said, you all will return from your 4 week vacation needing another vacation. Especially whomever does the bulk of the driving.
Since you're checking out the South Rim and Lake Powell, why not hook around and spend a few days at the North Rim? Skip Zion and head up to Bryce.
It's a pretty good haul from from Bryce to Moab, more than a day's drive towing a trailer. Coming out of Bryce you'll be driving through the former Grand Staircase-Escalante National Monument - which will soon be destroyed by energy exploration. Highway 12, The Hogback, is a fantastic drive, with as I recall, a pretty tall mountain pass in the middle.
Hwy 12 dumps you into Torrey Utah, Capitol Reef National Park - there's some fantastic petroglyphs you can see from roadside parking areas. Hwy 24 to hwy 95 out of Torrey takes you towards Moab. Along the way is Natural Bridges National Monument. Natural Bridges is a good overnight spot. They have a simple and inexpensive campground right inside the park.
With 3 days, spend it inside Arches, or inside Canyonlands... It's a long drive from one to the other, and there's more than enough to see at either park; they're both fantastic. Even trying to split the difference with Dead Horse Point, it's still a considerable drive to the Islands in the Sky (Canyonslands), or to the hiking areas of Arches (very slow road)
Mesa Verde, not sure how to make that work, it isn't close to Moab or Denver. If you wanted to skip Bryce and Moab all togther, you could head East after Lake Powell, maybe visit the Glen Canyon NRA, Valley of the Gods, Mexican Hat, Four Corners attraction and then onto Mesa Verde and your other Colorado destinations.
No comments about what to see in Colorado. Being anywhere near Denver makes me physically sick, I can't breath that filthy air.