Housesteads is at least 10 miles from Hexham (can't remember exact distance). You can get the AD122 from Hexham, the stop is about 5 mins walk from the train station. Vindolanda is further West than Housesteads and is set back a mile or more from the Wall route. It would be a good walk from Housesteads along some of the more rugged stretches & you could pick up the bus again to go either back to Hexham or along to Haltwhistle for a train back to Newcastle.