Hi Micheal,
I did this route ...the senda da orla Litoral...from Porto via Viana and Caminha and Vigo ...in June. I used the
John Brierley Portuguese Camino Guide book which is available via the UK CSJ Confraternity website....This includes all the Portuguese routes and majors on the inland route so I found it a little sketchy when it came to the coastline route.
However the CSJ site has just listed a new dedicated Guide from Johnie Walker at the link below...
www.csj.org.uk/product/camino-de-santiago-pilgrim-guides-camino-portugues-part-2-porto-to-santiago-coastal-route/
Other posts on this site also refer to Luis Freixos detailed maps. These can be found at...
http://www.caminador.es
I found some of the route not as well marked as expected but generally didn't mind going with the flow and enjoyed my Camino. But I would say if you want to do this route accurately throughout then you need to refer to good guides /maps from time to time.
Just to add that the ferry from Caminha to Spain does not run on Mondays.
Bom Caminho!