Day 1
It says that you are setting off from Santander on Saturday evening and heading to just north of Potes. We did this route, plus a loop of the reservoir at Rheinosa, and it was a fantastic route. But we set off from Bilbao early morning and got to Potes late afternoon. I think that you are being overly optimistic as, depending on just when you leave Santander, you will be clock watching and arriving in Potes late on. That is no way to enjoy these fantastic roads.
Now changed - we arrive about 6 pm in Santander, the same as a trip to the Pyrenees this year when we did 100 miles straight off the boat. However, I forgot we did a lot of fast main roads! Now shortened routes and will include some of the original route near Rheinosa on the last day
Day 2
In Gijon, you are missing the best bit: I would recommend taking in the Promenade and the Old Town at the western end of the Promenade.
West of Gijon and into Avilles, it is god-awful industry. If I were doing it again, I would just pick up the Autopista A8 and get to Luarca and spend some time exploring there. Also, as you get to Luarca,pick up the signs to the Lighthouse and enter that way, as that road gives good views and drops you down towards to port/marina area which is all but impossible to access from the towncentre as the one-way road system seems to work against you
Taken on your advice for promenade and lighthouse view. Going to stick with the minor roads below Avilles as on google they look good
Day 3
West of Lugo, if we were doing it again, we would leave the Ride route and just pick up the Autopista direct to Santiago. If nothing else, this would give you some time to explore Santiago, which I would highly recommend.
Now going to hit the faster roads west of Lugo!
Day 4
We did not drive out to Fisterra, so cannot comment. Between Pontevedra and Ourense, the Ride route took us along one of the worst sections of road surface we met. About 30 kms of really awful surface that shook us to pieces. We were in a car, so it might be more enjoyable on a m'bike.
Fisterra looks interesting (end of the world back in the day......) and will see if the road is still bumpy!
Day 5
Ourense to Ponferrada was enjoyable, but the final leg into Leon is bloody boring, as you are then onto the 'Plains in Spain'. leon was fantastic and worth staying a day at least
All good I think
Day 6/ Day 7
Can't comment, as we went north from Leon towards Bona, up to the reservoir at Valdehuesa, up over the mountains though Puebla de Lillo, before picking up the CL-635 and dropping down to Riano. These were epic roads and I would do them again any day.
I think our route should be similar to yours to the north
Your Day 6 route takes you to Cangas de Onis. But you miss out the ride up to the lakes at Covadonga. Don't just stop at the abbey at Covadonga, take the road up to the lakes. Not great riding/driving roads, as it is busy and narrow. But definitely worth the effort to get to the top to take in the views.
I included the trip already to the Lakes at end of Day 6 - bit hidden as Day 7 we head out
Day 8
I would take the A8 eastwards until dropping into Comillas. The N634 along here is no great shakes. Comillas is a nice place to take a break.
Might head to http://www.elsoplao.es/ and then do the loop near Rheinosa then up to Santander