I started both my 2013 and 2014
Camino Frances from St. Jean Pied de Port with one fleece zip front jacket. On my first Camino, I was compelled by the weather to buy a second, 1/4 zip pullover fleece to wear as an underlayer as soon as I reached Pamplona. Of course, I gave that away when I returned home.
So, naturally, on my second
Camino Frances, in 2014, I once again found a need to have a second fleece layer and ended up being able to buy an
Altus branded pullover on sale in Burgos.
I should add that my first layer for this past April - May Camino was a short sleeve Underarmour polo / golf shirt. I found the flip-up collar to help on cold and wet days and to protect from sunburn on hot sunny days. The two fleece layers were next, and the top layer was a Gore Tex rain jacket. I topped this off with a microfiber "buff." On really cold mornings, like when the temperature was less than 5 degrees (c) I usually switched to my heavier fleece watch cap.
When I encountered rain or snow I added my Sea to Summit Ultra-Sil poncho on top of everything. Yes you can encounter snow, especially at higher elevations into May. There was light snow at Cruz de Ferro on 16 May last year. Also, O'Cebreiro was lost in a white out, a very heavy snow squall, when I reached there in May 2014 as well.
So, in addition to fleece, be sure to bring a lightweight fast-drying warm cap and gloves. I prefer micro fleece and microfiber as they insulate even when wet, dry fast, and the gloves help with my walking sticks. I found a neon / safety yellow colored cap that is great for early morning road walking.
I hope this helps...