Hi mbarney. I walked February/March this year: Pamplona to Santiago, then to Tui and back to Santiago, then on to Finisterre. I enjoyed the cold, except for one brutal, wet day getting to Los Arcos. (My mistake there was to take spongy "waterproof" gloves, but if one stays dry all over, the cold is not really a prob.) If one is prepared to stay in the odd cheap hotel or pension, accommodation is available all along the track. I would certainly take a good sleeping bag, for those times when the heating is down or off. If the pass at Roncesvalles is closed or advised against, the alternative route via Valcarlos is a splendid walk in its own right. Just enjoy.
Buen Camino
Rob