http://www.crazyguyonabike.com/doc/?...oc_id=226&v=5z
I don't know about Santander specifically, but I have found cities in Spain all have excellent bike shops.
To inflate, bring a small pump then go to a service station to top up.
Refugios tend to fill up, so be prepared for that. You should make sure you have your Credencial (spelling? anyway, the 'passport' for the Camino) otherwise some places may not let you stay. That being said, there are LOTS of hostals and hotels along the route. I was initially going to cycle the actual Camino but with my regular touring bike and in the rain it was impossible for me. I have since hiked it and think that with an ATB maybe it could be done, though not everywhere. Probably best to run parallel in those cases.
B