I walked the Norte in 2022. The section from SS to Bilbao has variety. Some segments have rough trail i.e. stones, irregular surfaces. Some is road walking. There are steep ascents leaving SS. Steep descents as you enter Zarautz, Deba and Bilbao. And I mean steep, although you're mostly on decent paved surface. All along the route, there is a lot of up, down, up, down. Services can be long distances apart. There are areas of open exposure, where the sun can be pretty cruel. Despite and perhaps because of the physical challenge, the route is one of the most rewarding things I have done in the outdoors. You'll have lots of opportunities for solo walking, and majority stretches when you're out there all on your own. Great scenery.
Few Americans, mostly Europeans, some in vacation mode, rather than making a pilgrimage. Oh, and no drop offs that I remember. It is a route to savor. Lucky you.