Got another link for you!
http://www.so-utah.com/
I think the S. Rim, Grand Canyon has the better views. It will have more crowds and it will NOT be a place to be over the Memorial Day weekend!!!!
Two days at the S. Rim Grand Canyon will be plenty, unless you hike down to the bottom and spend a night. You will need reservations to stay at Phatom Ranch at the bottom. I think two nights, one full day is enough for the N. Rim.
Sequoia is 624 miles from the S. Rim of the Grand Canyon and then another 560 miles back to Zion. Maybe it's just because I've seen so many giant sequoia's in my lifetime, but I really don't think this would be worth it this trip. Maybe save Sequioa and Yosemite for another trip.
Instead of the Hoover Dam, check out the Glen Canyon dam in Page, AZ at Glen Canyon National Recreational area (Lake Powell)
If you could squeeze enough time, I'd spend two nights in Zion and one night in Bryce. You can leave Zion early one morning and be in Bryce in 2 hours. Both parks have nice campgrounds. If you are going to be at either of these places over Memorial day weekend, then make reservations! When you leave Bryce take scenic hwy 12 to Torrey, Utah and pass Capitol Reef National Park which also has an excellent campground.
Plan at least one day for Canyonlands and one for Arches. You can't drive through Arches. The scenic drive dead ends at Devil's Garden. When you leave Moab, Utah, you will want to take hwy 128 to Cisco, Ut and pick up interstate 70 here. This is a scenic drive that you will not want to miss!
You asked about Durango. If you don't mind back tracking a little from Rocky Mountain National Park , then I'd take the Million Dollar Highway (hwy 550) south from Montrose to Durango. This is a very scenic drive. If you could spare two more nights and one full day, then make it over to Mesa Verde National Park. Morefield campground in the park is very nice.
Have you considered Carlsbad Caverns in southern New Mexico?
Wildlife: Deer in Zion, Bryce & Capitol Reef. Not much in Arches and Canyonlands, unless you count lizards! Rocky Mts will have more.
Utahtea