Hi Jaycee,
Welcome to the board!
Have a look at these messages, as one our members "Pilgrim" just finished a Porto to Santiago pilgrimage.
viewtopic.php?t=148
It seems like "Pilgrim" walked Tui to Santiago in 5 days. Tui is just inside the Spanish border, have a look at this map:
http://www.galinor.es/llegar/m-galicia.html
Regarding starting points in Portugal. On a trip (by car) down to Porto a few weeks ago, my wife and I stopped in Braga and really fell in love with it. It has a nice old town and cathedral.
Alternatively, on the border between Portugal and Spain there is an old fortress (La fortaleza) that has markets every weekend. From there it would be a 10 minute walk to Spain; it's just across the river.
Anyone with any ideas about a good starting point in Portugal?
Greetings from a rainy and windy Santiago,
Ivar