davebugg, I tend to have an different opinion about booking ahead. (no shortage of opinions on the forum)
I booked every night of my 3 week journey and found no small amount of comfort in knowing there was a bed ahead with my name on it. When I experienced an injury, I chose to cancel or reschedule only a couple of the reservations. It turned out to be a better plan to walk as far as possible each day and use bus, train or taxi to get to my evening destination in order to continue on the timeline we had set for Santiago. Especially since we had a return flight back to the US that would not wait for me to heal.
I can not imagine setting a pace each day to accommodate the slowest of the group. In my mind, having a goal for each evening would work better for a group and allow each one to determine how and when they arrive. Similar to the arrangements of a tour group.
So Steen, with regard to your original question, I would also recommend booking ahead, and looking for reservations that are changeable to allow for flexibility in the event of those possibilities outlined by davebugg.
Bon Caminho