A few years back I rode quite a bit of what you are about to do, but over two trips. I did the eurovelo route, but started from Lourdes (which was an experience). Also from Santiago to Biarritz. Really enjoyed the region you’ve just passed through. The section from Biarritz to Bilbao was fantastic though, loved that.
If you decide to keep going in Spain you’ll pass the largest sea cliff nesting colony of vultures in Europe – you’ll know when you are there as they fly just above your head in considerable numbers. I followed the northern most Camino route along the Spanish coast. Lovely people, awesome food and stupidly cheap – had a 3 course dinner, with a full bottle if red, for 12 euros on one camp site (possibly Santandaer)