We've done the trip quite a few times, starting from Florida. We would generally be in Arizona late on day three. But we used to push hard on the first three days since the area that we wanted to spend our time in started at the end of day three.
That meant an early 7AM start and driving until 8 PM or so. 700 miles a day or more. Trading off drivers helps a lot. Once we hit our target area we slow down to 250-300 miles/day and enjoy ourselves. Now that I've retired we have given up on the 3 day push at the beginning of the trip. It just didn't make sense for us to waste all that time stopping in Big Frog PA for the night and missing a day at Bryce or GC.
You are probably a bit farther away and there aren't any direct roads, we just run down I-10. You'll have to zig-zag around going southwest diagonally. So maybe 4 days for you.
Four Corners and Grand Canyon are a day apart if you take it easy and stop at some of the places you'll pass along the way. You probably need a Navaho guide at Monument Valley and I'm not sure you'll want to drive your Class A down those roads.
Tombstone is way south of the other areas and it's just a tourist trap. Maybe 4 or 6 square blocks in a small town packed with 'tourist attractions'. We've been there a couple of times, not as a destination but just because we were in the area at Chiricahua National Monument. I'm not sure when you plan to be there but from late April on it is very hot so carry a water bottle with you.
You'll pass a lot of excellent National Monuments along the way.
I'd plan on spending a 5-7 days at GC and a day or so at the other stops. And we like the North Rim of GC a lot more than the South Rim which has 10 times more people. The sights are the same at the North Rim except there isn't that Indian reservation.
BK