We need to be at the Orvieto train station early in the morning before the funicular opens for the day. Is there bus service to the train station from the city in the early morning? Or, must we take a taxi?
It would not be a very long taxi ride to the station, so for an early morning departure, you're probably better off arranging a taxi with your hotel the night before. Then you don't have to worry about making connections. I don't know where you are staying, but on google maps it shows that it is 5 km, or 8 minutes from the Duomo to the train station.
sara,
I agree with the previous reply. Ask you hotel to arrange for a Taxi at the appropriate time. That's the easiest solution.