My reply would be to get an architect that is local to you as he will have to deal with your town hall. Look at the directory of registered architects for Lugo province here -> http://www.coaglugo.es/gl/directorio-socios/
It doesn’t mark whether they speak English but the important thing (unless you are going for a culturally significant build) is to get a good local architect.
You could try emailing the Galician College of Architects (http://www.coag.es) to see if they know an English speaking architect but I would be very surprised if they knew that level of detail for someone that is close).
If your project is sizeable, then you will probably need a Technical Architect also.
I’m sure there are some long established Brits in Riviera Sacra that you could track sown and ask.