I'll just add that the 634 between Santander and San Sebastien has some spectacular coastal roads - really wide, great condition and amazing descents. Means you head a bit further north before you really get into the Pyrenees but that's no bad thing if it means a visit to Bilbao /San Seb etc.
Lovely, thank you. Great photos from you and from @edscoble
Ed's route from Santander to near Lourdes looks like it could be good for the start of the trip.