Hi, ritopaxi,
I've seen anglulero's comments on what seems to be a duplicate thread of this posting:
el-camino-del-norte/topic19692.html
Here's what I can add to what s/he told you:
Though Gronze lists Sebrayo as the starting point of the stage, I'd just start in Villaviciosa. I don't think that those 6 kms from Sebrayo to Villaviciosa have any un-missable points. That would make Villaviciosa to Pola de Siero a very do-able 24, which would allow a short detour (down and up 300-400 m I think) to the church at Valdedios if you were so inclined.
From my 2007 notes, Villaviciosa to Pola de Siero is all asphalt, but nothing busy. There is an albergue in Vega, about 9 kms before Pola de Siero, but there is apparently a new albergue in Pola that is very nice. From POla to Oviedo is only 17 kms, again almost all asphalt but only one highway spot.
Oviedo to Aviles (28 kms, which you would be doing in reverse) is where we lost the camino. My notes tell me that it was in La Posada de Llanera where no one could tell us anything about the camino and we just stayed for 17 kms alongside the national highway north to Aviles. Not a nice walk.
So if your choice is Aviles to Oviedo or Villaviciosa to Oviedo, I think the latter route is much more pleasant, though both are nearly all asphalt. Starting in Villaviciosa will take you two days, whereas you can walk Aviles to Oviedo in one but unless the camino has been well marked it could be a very unpleasant walk on the highway.
Buen camino, Laurie
p.s. in your note to Angulero you asked about walking on the autopista. Don't worry, you can't walk on the autopista, it's strictly prohibited the worst you will find is walking alongside the national highways.