How many people in May

Wastemaitime, Hi - I'll be heading out from Bilbao on the 19th, and will hope to hear how you're getting along should you post. I'd like to not do much booking ahead as well. You're probably on your way there - Buen Camino to you.

In May 2016, 1,480 arrived in Santiago having walked the the Norte. 155 of them started in Bilbao. This went up to 2,268 arriving from the Norte in June, but that's still less than 10% of the numbers on the Frances (25,625 in the same period!)

https://oficinadelperegrino.com/en/statistics/

The Norte doesn't have the same pilgrim infrastructure as the Frances, so beds are sometimes tight as there might be only one albergue in town. However as its a coastal tourist route there are usually a couple of cheap-ish pensions nearby so it shouldn't be too much of a scramble.