Hi, Sophie, Welcome to the Forum! We have a happy little band of Invierno veterans who are always quick to jump in and answer questions. I would start with two things. Scroll through the Invierno subforum and take a look at the threads with lots of advice and recommendations. I assume that's easy to find and you have access to it, but just in case you are as tech-challenged as I am, here is the link to get you to the top of that subforum.
https://www.caminodesantiago.me/community/forums/camino-de-invierno.79/
Look particularly for posts by ChinaSky, who is the one recent pilgrim I remember who walked in winter last year.
The other thing is to look at the forum guide put together by us Invierno fans. I am right now working on updating it for 2018 and may be done with a new edition by the time you leave, but the changes I am finding so far are more involving things like changed opening hours, bar and restaurant availability, a few new lodging recommendations, etc. That guide is here and can be downloaded. It will give lots of suggestions for stages, accommodation, etc.
https://www.caminodesantiago.me/community/resources/camino-de-invierno-2017-edition.535/
As far as gear, you should go prepared for cold and snow, I would think, though I am not sure how much you will actually get. Just bring what you would bring if you were walking any of the Northern caminos in winter, I know there are threads with gear suggestions for walking the Francés in winter, and I think those recommendations would apply to you as well.
Happy to help if we can, so just let us know. Buen camino, Laurie