Cross Country South
Trains are Virgin Voyagers - four or five coach trains with a first class coach at one end and quiet coach at the other. There is an onboard shop selling drinks and snacks (most of which are free for first class ticket-holders), and other assorted rubbish. Because these trains are short they can get very busy even outside peak times, so unless you want to stand you should reserve a seat even if you have a railpass.
Virgin Value tickets are advance purchase tickets which are much cheaper than the walk-on fares. In theory they are available for all Cross Country services until 1800 the day before travel, though in practice the cheapest ones are gone weeks before travel, and they often sell out completely a week before travel.
All trains in Britain are completely non-smoking. Many stations in Scotland are also non-smoking, so you will be unable to take advantage of prolonged stops at these stations to stand on the platform and smoke.