The coastal caminho offers a variety of public transport inside Porto City, e.g. the Metro to Matosinhos.
After that you are heading to the coastline, which means less buses, no train. During summer you pass a lot of open cafés, but in September/October it becomes much less.
From Vila do Conde to Povoa you have a parallel train line which you don't see while walking (500-1000m to the east). Soon you are leaving Porto metropolitan area and again you are following the coast.
I remember buses passing me in Fao/Esposende, but I'm not remembering their destination.
After that I think you have to get to Viana do Castelo somehow. From here the railway runs in parallel to Valenca with stops in any mayor village. Some bigger places have also bus stops of rede-expressos.
October can be windy, rainy, misty and cold or even summer like with ~30°C from time to time. If you like more stable hotter weather start earlier. After some rainy weeks in October/November winter weather tends to be colder but mostly dry (without warranty). The area of Santiago is famous for rain all year round, but Vigo / Pontevedra is not so bad.