I imagine you'll be travelling quite light so I recommend at least a fleece and a waterproof jacket. Layers are good. Thermals are even better cos they pack down very small and are very light so a thermal vest and thermal longjohns under everything and you'll be cosy as toast!

As for booking in advance, like you say its not high season so you should have no worries just that November is when some hotelier might have their holidays after the summer rush and before the winter one, but hell you're not going to the back of beyond.

There are lots of nice clean ordinary hotels open all year round for business people so you should find no problems at all. Have a good trip.
I'm on holiday in Castille and Leon at the moment and being September I expected some sun and heat.It has been cold since we got here so I'm glad I packed a wooly jumper, which was originally for nights only, and a fleece.