@Lizbird58, I walked the CP in May using the Central route.
1) Where is the best city for an extra night stay- Pontevedra or Caldas de Reis - why?
I didn't stay in either, but if pushed, Pontevedra looked to be a more interesting town than Caldas de Reis. Would it be best? Your call.
2) Would you break the walk from Padron to Santiago into 2 nights or would you prefer to power through and spend an extra night In Santiago - why?
I walked from Arcade over four days to spread out my walking days, and stayed in Glorioso the night before reaching Santiago. I am slow, and I wasn't in a rush. But at about 12 km to go, it would be possible to get into SDC in the morning with an early start and a brisk pace. I didn't, and went to the midday mass the following day.
I was also able to spend another day in Santiago, and took a tour out to Fisterra and Muxia.
3) How far in advance would you make your room reservations?
I booked accommodation in Santiago before departure, but where I could book along the way, that was normally the night before, maybe two nights. Someone else might give you a better idea of what might be needed in October.
I use a CPAP machine, so I like to check that I will be able to get a bed near a power-point, or a private room if one is available.
4) How far in advance do you book your airfare (I'll be flying in from New Mexico - no hubs here) but think 10 months ahead is too early to book? I will pay extra for a changeable but non-refundable ticket.
I start looking for specials about 11-12 months out from when I want to travel for the major flights into and back from Europe. I normally visit family and friends in the UK after my camino, and don't book those flights more than a fortnight out from reaching Santiago.