vwzoo,
In the happy, easier past years, 2007, 2008, 2009, and 2010, when I walked the CF late autumn /winter accommodation started to close mid October but some place was always open. There were no summer crowds and beds/bunks were available. I usually slept in albergues, often the sole pilgrim, but also in back rooms of an open bar/restaurant.
Walking off-season during those past years I rarely saw more than 20 pilgrims at one time. There usually was a strong sense of camaraderie amongst those of us on the route especially during storms or difficult stretches.
Difficult CF stretches after storms could be; the Valcarlos route up to Roncesvalles (the Napoleon route is closed from November to April), across the Montes de Oca from Villafranca, Najera to Santo Domingo de la Calzada, Monte Irago and, of course, to and from O Cebreiro. You must be prepared for
snow in the mountains.
Do carry simple non perishable "extra" food. Spain is filled with delicious stops, but all are not always affordable nor open; the one food shop in town may be closed on the same day as the only resto/bar. No joke.
On past winter caminos especially during storms when I stopped in small and remote albergues far from any supply source novice pilgrims often staggered in wet, cold and hungry. They may have had the best gear but carried no food!
Of course I shared; a chunk of cheese and wedge of sausage with a few dried abricots can be ambrosia in such a setting. A smile returned by a new friend over a simple meal is one of the Camino's many joys.
Happy planning and
Buen camino to both of you.