Hi Heather!
November will be very quiet by Sarria's standards, but there will still be pilgrims around on that stretch. To avoid disappointment check about opening dates if there are any places you particularly want to stay in, but if you're not fussy there should be plenty of cheap beds. I'm not sure about Santiago - Finisterre in late autumn. When I walked it a couple of years ago it was a bit earlier (early October) and there were plenty of places open then.
I've no idea about trains from Paris, and flights to Galicia are limited. Vueling don't start flying to Santiago until December, unfortunately, but they do fly to Asturias.
Villafranca would be a good starting point and allow you to see O Cebreiro, which is a highlight.
Brierley's guide book suggests that it takes 3 days from Villafranca to Sarria, including walking from Villafranca to O Cebreiro on the first day. I've never done it that way, as it's 30kms with one of the most challenging climbs of the whole Camino right at the end of the day! You might want a shorter first day (maybe stop in Vega de Valcarce) and tackle the climb to O Cebreiro the following morning. You can make up the time in the following 2 days.
Good luck with your preparations. Buen Camino!