I have added the tag "winter" to your thread. Clicking on it should lead to many threads about preparing for a winter Camino.
What do you think would be warm enough while walking in winter at home?
I haven't walked the Camino in mid-winter, but I walk regularly in winter at home. I think that the layers you describe would be versatile and warm enough - several merino layers, puff jacket or vest, waterproof shell, along with buff, beanie and gloves. Make sure you have some wool socks in case your feet might get wet. I would add a pair of waterproof mittens over the gloves, although dishwashing gloves might do the job as well.
Also be aware that you should always keep one layer dry to wear in the evenings at the albergue. This isn't usually a problem because the coldest weather is more likely to be dry. So, when you need all the layers for cold, hopefully you won't get wet while walking.
Walking does generate heat, so you will likely find that you start off with many layers in the morning and soon need to remove some. So, keep that in mind as you layer up. The buff and beanie are easy to remove quickly after, say 30 minutes, but you may need to stop and remove your backpack in an hour of two. You do not want to get sweaty!