Aw I love rotties. We used to take care of one sometimes and we almost adopted her when the owner thought he's have to give her up. (He eventually found a place to live that allowed her.) Your property is beautiful too.

Basically I don't think there is a good way at telling how large a puppy will get when you don't know any of the breeding. I know quite a lot of people who were surprised at either how much or how little growing their puppy ended up doing.