Sounds like a great itinerary. The South Rim is certainly closer for us to visit, but we love the solitude of the North Rim.
If you're coming up to the North Rim from Flagstaff, you'll want to add Sunset Crater and Wupatki National Monument (same road connects the two).
Hoover is certainly more famous, but you can also do the dam tour at Glen Canyon in Page, AZ. If you've seen one dam, you've seen them all... The only concern might be the detour, but that's also part of the adventure.
A side benefit of going to Glen is that you'll have no excuse to go see Las Vegas unless you really want to. Personally, I'd stick to the national parks and avoid it.
Now, a question... are you planning to tow a vehicle, or just do everything from the motorhome? It's certainly doable without a tow vehicle, but you may have a few more opportunities with a toad.