This is not going to be super helpful but here goes. I've been to this festival almost every year since 2012 (missed 2016). Always camped and I consider the camping site to be half of the festival's experience. It's in a pretty idylic scenario near a small village in the north of Portugal. I would strongly recommend going and camping. If you want a bit more comfort there are glamping options, but being near the river is priceless in my opinion.
if you really want the hotel option it's a bit more complicated since it's a very small village. There areno big hotels in it and the small inns available are generally fully booked a year in advance by the festival's organization for personell and artists. There may be some airbn'b options still available. The only shuttles I know of go from the village to the festival site so this is also not very helpful for your situation. Consider camping or renting a car and driving to and from the festival.