Much has already been said here and I missed this thread till now. Still, every couple of years I spend a week or so out there (like cblaisd but I go there to hike and get away from the roads).

Do get a National Parks pass at your first part, instead of paying the entrance fee. It will cover all your other Federal park lands, which is most of what is on your agenda (Snow Canyon and Kodachrome Basin are state parks, but I don't recall paying anything in Snow Canyon anyway).

I'd just add, with the discussion of your itin around the 19th, why bother with St. George? Nothing against the place, but its a town and you're looking to spend time in parks. The temple there is scenic and historical but unless you're Mormon you can't go in.

Better would be to stay near Zion, and spend an extra day around there (maybe one day in the main canyon, and one day up on the Kolob Terrace area if it's not too cold). I know it as a hiker more than a driver to be honest. But even a non-hiker should do something like the easy walk to the Emerald Pools in Zion Canyon.

From Zion you're that much closer to the North Rim. I actually stay in east Zion at the Thunderbird Lodge which is where those 'Ho made pies' are served. I think the rooms are pretty good and I really like east Zion - do walk the short Canyon Overlook trail, it will blow you away. And from east Zion it's that much closer to the Canyon....

Nice time of year to go! I was just out last month and believe me, it's hot!

Oh, and Canyonlands, yes the Islands in the Sky district is easily accessed from Moab and what amazing views!