@JamesPaulG, welcome to the forum.
The Primitivo is my favourite route, but I have to say not one I'd want to walk in winter.
Predominantly because I hate snow.
Statistics show that the Primitivo is not completely empty during December : last year apparently 286 pilgrims completed the route in December, significantly more than I had anticipated. So hopefully you will get the company you desire.
There are a few forum members who have walked the Primitivo during winter, hopefully one or two of them will see this thread and chip in with useful advice.
I recall this thread:
Thread 'Short documentary about Camino Primitivo in winter.'
https://www.caminodesantiago.me/com...ntary-about-camino-primitivo-in-winter.81636/
You could always PM the author for advice. (Although you will have to post at least three more public messages first, newcomers cannot access the PM function until they've posted at least five times)
It would be especially helpful for future pilgrims if you would at least post a short summary of your walk once you are done.
We armchair Walkers would of course love a daily update, but I fully understand if you have no desire to post once your day is done.
As to
@davejsy 's comment regarding accommodation: many Albergues have already closed for the season, and won't reopen for months. A quick search has shown that there appear to be options available however. As usual, Gronze is the pilgrims friend in this regard. In some instances it may be that you have to reserve the day before in order to ensure the heating is on and somebody is available with a key; never having done this route in winter I do not know.
Food would be more of a concern as it appears to be pretty typical for some of the smaller places to close at some point, or at least operate very limited hours - perhaps even just one or two days a week. Personally I would ensure I was carrying a full 24 hours worth of food.
James, assuming you've done your research and are prepared for the conditions you may encounter (whether it be loads of snow or loads of mud), all that remains is to wish you a wonderful Camino!