In general, there aren't that many people in the winter (Jan) and most of them are on the routes with more pilgrim infrastructure (Frances and Portugues). I'm not sure how much infrastructure will be open in January. I've heard that in the summer the Camino can be crowded with beachgoers and these can compete for places in the accommodations. That competition may not be a thing in January, but by the same token a lot of places may be closed in the "off season".
Compounding the fewer people due to low season will be the fact that you seem to be planning on walking away from Santiago de Compostela instead of towards it, and all other pilgrims you meet are likely to be walking in the opposite direction. That means that instead of meeting the same people day after day and forming personal connections, you are likely to meet them for a few minutes only (on the road) or one night only (in accommodations).
On the other hand, swimming against the current, as it were, you will meet more people in total although very briefly for each, as you interact each day with new people rather than walking more or less with the same group.