So, early happy 40th B/D Rick K. I have done the whole thang, it can be a real sweet ride if the weather cooperates.
Some things to consider: AJ's advice on sched, speed and so-on is gold. We have both learned it the hard way, you don't have to. We took a week to do it, the layover day in the Blues was worth it.
I did it with a support vehicle that took all food, BBQ, campo gear, beer and gas to a fwd campground. That was totally worth my fraction of the RV gas to do so because I got to ride an unladen bike, just water, power bars and spare tube. Which is another important point:
If you ride an unladen bike, not only is it way more fun/safer, but your risk of pinch flats goes way way down. Pinch flats are probably the #1 ride-killer for large groups of laden bikes going places they haven't been before, wastes a lot of time, unless you are careful to pick scenic spots to have a flat. In my experience, that happens only one out of five.
Ride it south to north, sun will be behind you, way easier to see.
The southern end and northern end are really good, don't blow those off.
Southern end has a section that goes to 2nd highest road in the state, just east of Lakeview.
The northern end has a section in the middle Walla Walla River canyon that is so narrow, exposed and scary I will not do it again; you have to ride that!