I walked Porto to Santiago in Apr last year, loved the country and people so much that I returned to walk Santarem to Porto at the end of Oct. Porto to Santaigo is a very safe stretch to walk on your own, it's always busy and you see pilgrims ahead or behind a lot, especially after Tiu. I started alone from Porto but then walked on and off with some people. If you don't feel like walking alone you could always find a walking companion on the road. Lisbon to Porto stretch is a bit different though, longer stages, fewer pilgrims. I started walking there on my own, felt safe, then met some people on the way and felt very comfortable walking with them, so 4 of us decided to walk together to Porto. That was the very end of Oct, at the end of the season, and apart from our group there were 2-4 more pilgrims on the same stage at a time, so you are never alone. We'd talked to hospitalieros on the way and they said that Lisbon to Porto is getting very popular now, there will be even more people walking next year. I came back to walk Portugues Interior route from Viseu this June, we walked alone for 8 days, very rural, very picturesque and also felt very safe. Now am looking at other caminos in Portugal for the future as the country is beyond amazing! Bom Camino!