You will definitely need a car.
My wife and I took the train from Porto to Pinhau. We then took a taxi up to the hotel. We stayed for two nights and didn't have a car. During our stay, we did the tour of the Bomfim winery and a boat trip on the Douru River. We were fine without a car because we wanted some down time to just relax. A car would be nice if you want to explore the mountain roads and do tours of the many vineyards in this area. And if you are planning to stay for more than a day or two.
The Casa is a great place to stay. Have fun!
Get an answer from Casa do Visconde de Chanceleiros staff and past guests.