This is the important part about a roadtrip. It has to go where you want to go.
I think your plan will work, especially if you visit some of the NPs when driving your chosen routes. I would still leave some flexibily for last minute change of mind.
The large scale is a bit bulky and heavy, but it is much easier to read. What I do with my Rand McNally to make it a souvenir of my trip, each night I sit down and hilight each and every road on which I travelled. It is great when you later look back over your trip, or when sharing with others. When I look through mine it is almost as if I am driving those roads again.I will be having the Rand McNally Large Scale Atlas for Navigation but i still would like to have google maps as a backup. that is why i am still working on the kml file. And i promise it is just a backup.
Have a great trip.
Lifey