We have been told 10/12 miles per day is what we should be aiming for
That is typical. At times you may be capable of more. It is hard to describe the physical "ups and downs" of walking the Camino, but you are likely to feel pretty good the first day, quite sore for a few days, then recover to a higher level as you become more fit. Then you may "hit the wall" nutritionally as your appetite decreases and weight drops. After a couple of weeks, you may begin to combat mental issues. Your enthusiasm lags, the weather gets to you, or the bed race has you in turmoil. You may perceive that you physical conditioning has improved so much that you can walk longer than before, push past a limit, and cause shin splints or other injury. Joints and connective tissue do not recover as muscles do, and this is most apparent in those over the age of 40 (and even more so over the age of 60).
The
Camino del Norte has a lot of up and down. The views are beautiful coastal views, though it is possible to reach a point that you have seen enough water. Stages can be longer than on the
Camino Frances, but there are fewer pilgrims per bed. By September you probably will not have a problem finding a bed each night, but there still will be a lot of pilgrims.
I won't hazard a guess on "the most scenic route." There is too much variety on each of the routes for there to be a "factual" answer to that. I personally liked the Meseta, where there did not seem to be a tree in sight. Scenic? Well, yes, in its own way. The green valleys of Galicia are quite beautiful. Scenic? Well, yes, as a break from hiking in the hot sun, but often obscured by fog, so you may not see them.
Have fun; take your time; don't push age-appropriate limits. You will love it.
Meseta:
http://www.youtube.com/user/YourCamino# ... KmTqaZSnpU