@Jaujauzimbo
The (international) buslinks from Lisbon or Porto do not stop in Ponte de Lima
the first stop from Porto Airport is Valença do Minho so you have to go back from there to Ponte de Lima what is about 40 kms. Last month when I waited for my bus to Santiago in Valença I noticed a bus in the direction of Ponte de Lima but it does not go very regular. The public transport system in the north of Portugal is not very well developed.
I have a far better solution for you if you have time !
invest your time in the best place to stay at the entire Caminho Português.
If your hike is calculated in advance e.g you will do Ponte de Lima to Santiago in 10 days , add one or two days to it .Go from the airport by metro to the Batalhã railwaystation In Porto Take the train in the direction of Barcelos , Viana do Castelo , Caminha and Valença do Minho
go out the train in Tamel ! One stop after Barcelos.
you are right on the Caminho and follow the waymarkers ahead for 6 kms and you will be at privat albergue Casa da Fernanda in Vitorino dos Piães.
An unforgetable stay . Next day walk to Ponte de Lima ,14 kms. A good warming up for your caminho.
Bom caminho