I have just come back from doing this. Ecxellent choice! I cannot give you advice on albergues - as we were a considerable family group ( my two daughters and four grandchildren between 17 and 10) we preferred to stay in cheap hotels of which there are plenty.
As to the signs we stayed systematically on the cycle path which runs right next to the river. The camino goes inland a bit on various occasions. It was extremely hot at the time (40 degrees), so we had a dip in the river once.
In Valença we came along a wall which was a sort of fountain (had not seen that on a previous occasion). Water washes over it the whole length and in this hot weather everybody lent against it, front and back, and got sopping wet! What an experience!