Well, NWC -
You is still young.
If you are leaving early-ish - early to mid May -
You might consider driving east and starting from the Atlantic coast.
That way you might miss some late bad weather in the Pac NW
and miss the late summer heat in the East. (Which is brutal, btw.)
A later start makes sense west-to-east.
I am a big believer in water's edge to water's edge.
Preferably with ocean waves and sand.
Harder on the east coast than the west, but doable.
The sag wagon will come in handy many times.
But it precludes you from hiker/biker options in national parks.
Many park campgrounds are already booked solid for this summer.
It may require a more fixed itinerary than usually comfortable.
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One idea -
Since you have the sag wagon, cross at I-90 at Vantage.
Then shuttle to the boat landing at the bottom of the Old Vantage Highway.
Riding up thru the columnar cliffs is supreme.
(And I would think it qualifies a s"legit" X-USA.)