I wouldn't worry about the steel string demon. As a fiddle player, you probably already have callusses that will do just fine. If you find you need to work up to the higher tension on a guitar, then I recommend silk and steel or (nicer) silk and phosphor bronze strings. The treble strings are standard steel, but the wound strings have a nylon filament core similar to the ones on a classical guitar. Lower tension that standard steel strings and a nice warm sound. I still keep them on my "starter" guitar (a $250 Alvarez RF-20), since the action is a bit higher and the neck not quite as comfortable as the setup on my Martin.