Get a train from Paddington main line to Newport (South Wales), which is 2 hours max. Change and get a train to Chepstow Station.
You need to pre-book a taxi from the station. (it is approx. 2.5 miles from the station).
There is a pub within walking distance (10 mins) and a farm shop selling everything (meat, cheese, milk bread, chocolates etc) about 1.2 miles away.