Reddit mentions of A Pilgrim's Guide to the Camino Portugués: Lisbon - Porto - Santiago / Camino Central - Camino de la Costa (Camino Guides)

I'm planning on doing a very similar route this September/October. I'll be starting in Porto and following the Senda Litoral to Vila do Conde and then will be taking the regular Coastal Way to Caminha. I'll walk along the River Minho and join up the the Central Way at Valenca.

I ordered the John Brierly book called A Pilgrims Guide to the Camino Portuguese. I'm pleased with it because it has very nice maps that include the Senda Litoral (as well as the regular Coastal Way) and it lists all the relevant accommodations/albergues and their prices. However, it does not have much descriptive text about Coastal or Litoral routes if you want more in-depth information. IF the Senda Litoral is well way-marked, the maps in this book would probably be sufficient, but I've gotten mixed-messages on that front.

Have you tooled about on Google Earth? I've found TONS of GPS tracks for the various routes-- some seem more accurate than others.