I have ridden most of the Norte and also hiked & biked with a friend some of the Transadaluz in S Spain (I was the biker). It might be useful to understand his style of riding and also the type of ebike he will ride. After all there is a huge difference between an urban rider on a "Dutch" bike and "sporty" rider on a full-sus trail bike. Also does he intend riding the Camino or following the road option?
Here are a few suggestions for you & your friend:
* he might consider riding more of El Norte starting further east as there are some great rides in Pais Vasco & Cantabria then join you further west.
* he might consider taking a normal MTB (hard-tail or full-sus) to go slower, carry less weight and eliminate the need for recharging battery every night.
* he could meander more (use komoot to find local trails), visit places of interest along the way, sort out accommodation for you both as he will have more time, do the shopping, scope out eating options.
* there are plenty of journals on the www, my journals are posted on crazyguyonabike using the name "skinnybiker" but there are others.
Finally remember you don't have to stay at the same hostel / hotel every evening, he's on a bike so a few kilometres is no problem.