From Villafranca, you can definitely find places 10km to SdC. Use booking.com and gronze. But there are other considerations. Than distance. While surely not insurmountable there are some hills and a moderately steep short decline into Portomarin and Triacastela.
If you are traveling in September make reservations. The towns fill up. Since you have an idea of how far you can walk,plan accordingly, especially if you want a private room.
Watch when you make reservations that you there is food available. Some places will not have food in their location, but just machines. They might be two miles outside a town with no real sustenance and really no cooking facilities. Also there are a couple of clunkers along this route. So use booking.com and read the reviews. The services available will also be listed.
Use Correos.com to send your bag ahead! Correos is the most economical when walking short stages because they charge you a flat fee from a Villafranca to SdC…regardless of how many stops you make. The more you stop the more economical it becomes.
@Anniesantiago posted a great idea of obtaining taxis! As you pass through towns. You will see taxi info posted in the various tiendes and bars. Take a picture of them should you need help a you can call for one.
Going up to O Cebriero might be a bit challenging for you. It is a climb up to top. There are alternatives. There is a bus, I believe that stops in Ambasmestas on NVI ( Alsa.com) Or you could order a taxi to the top. It can be quite full up there, so if walking in September, definitely make-reservations ahead.