I wanted to check back in and thank you all for your advice and let you know how it went. I got extremely lucky with the weather and the November 1 holiday making it feasible to get to Potes, although I wasn't able to make it to Espinama because of my timeline. Far from being an isolated route, I found it very busy because of the unusually warm and sunny weather coinciding with a 4-day weekend. I encountered 16 other pilgrims on the trail, most of whom did it in 3-4 days.
Because of the shorter days, the morning fog the first few days, and a strong desire to avoid getting caught in the mountains in the dark, I took more time than most accounts I've seen:
Day 1: San Vicente de la Barquera to Serdio - In San Vicente, the tourist office couldn't give me any information beyond the map that you can get on the Camino Lebaniego website, so I figured people in Serdio were more likely to have information and I could make a decision about whether or not to go ahead. The hospitalera there (Katy?) was very busy with preparations for the Chestnut Festival, but was able to tell me that the bars in Cades and Cicera open only on the weekends in the fall but would both be open while I was there and I shouldn't have any trouble otherwise.
Day 2: Serdio to Cades via the Senda Fluvial - This is an absolutely lovely walk, mostly off-road. The Cades albergue is small, only 8 beds, but there are plans to add more beds for next year. In the meantime, overflow pilgrims can sleep on the floor (there were 10 of us this night).
Day 3: Cades to Cicera - The municipal albergue opens when you call and is set up for many more people than will ever use it. The one year-round bar in town does open on the weekends for both lunch and dinner but opens very late in the morning, so be prepared to either carry breakfast or purchase coffee/biscuits the night before.
Day 4: Cicera to Potes - There are a couple of ways out of Cicera and the waymarking was a little confusing. A group that intended to go on to Cabañes the night I was there ended up getting lost and having to bushwhack down back to Cicera just as night was falling. We took the route out the front of town, heading down by what looked like an old mill before starting to ascend. I believe this is the Canal de Franco I've seen referenced in a couple of accounts. It seems to avoid the Collado de Arceon, since we never came out on top of anything and none of the trail descriptions match up, but it looks like it meets up with the trail down off the Collado under the power lines.
Even if you're not staying at the private albergue in Cabañes, it's possible to call ahead and arrange lunch, which is what we did. It made a great stopping point and alleviated the need to carry much food.
The way out of town is marked in two directions, and we took the way that descended immediately. It's mostly pavement into Potes, but all relatively quiet minor roads or the multi-use path along the river that finally gets you into Potes.
Day 5: Potes to Santo Toribio and back - The albergue at Santo Toribio seems to be permanently closed, but you can still get your Lebaniego at the gift shop and the albergue in Potes will let you stay a second night. The Potes tourist office staff (who manage the albergue) were incredibly kind and helpful. They do have a short guide to the Vadiniense that I picked up for future use and can post a copy of if it's not against forum rules. Potes itself was busier than I expected, but that's likely because I arrived just before the large annual feria del ganado on November 2. I wish I could have stayed for it, but had to leave that morning in order to catch a bus. Bus connections from Potes are only to Unquera, Cabezon de la Sal, Torrelavega, and Santander (and possibly one other town that escapes me right now). I was told that there used to be bus service to Leon in the summer but that it was discontinued in the last few years.
Overall, it's a remarkably beautiful Camino filled with very friendly people and I'm glad everything aligned for me to do it. I hope to return in another season to complete the full Lebaniego/Vadiniense combo.
