There`s a bunkhouse at Barrowburn, next to the tearoom, you could do self catered accomodation in there and you are at the end of a couple of big loops of riding. Barrowburn is just up the road from Alwinton, which has a pub that does good food and good craic, the landlord rides a bit as well.
Sandstone way has more tarmac than an MTB rode should have ;)