The walk from Combarro ( a most interesting village) to Armenteira is very tough! At least it was for us, walking in intense heat. It's a hard climb, which at least gives you some stunning views. There is no place to get fresh water. You must take both water and something to eat with you. We stayed at the Albergue in Armentiera.
We were all pretty well shattered, by the time we arrived in Armentiera, but I put part of that to the excessive heat (35 deg. Plus). The next morning, the walk down along the river, going from one water mill to another ( el Camino de la Pedra y del Agua) was absolutely beautiful and almost magical.
The boat, in our case was one for 8 people, leaves according to the tide. We left at 8 am, so were fortunate. We stayed in the Albergue in Vilanova de Arousa, where we booked and paid for our places on the boat for the next morning.