I won't go into too much at this point because it is past my bedtime, but a couple of things.
When you mention a town, particularly if asking for directions or regaling locals with where you have been or are going, use the whole name. There are often similarly named towns or villages nearby and only using part of the name will confuse or perhaps cause comment. Bourton-on-the-Water is one way from Stow-on-the-Wold (where the wind blows cold, used to be said by my father who lived a short walk down the hill, and by my great aunt who ran a pub in Stow-on-the-Wold) and Bourton on the Hill is about the same distance the opposite direction. Call it Bourton and take your chances. Same with the very popular with Americans market town of Chipping Campden. "Chipping" is Old English for market or marketplace. Another market town on the road from Moreton-in-Marsh towards Woodstock and Oxford is called Chipping Norton. Call it just Chipping and see what happens. I see you have already discovered the two Slaughters (whatever you do, do NOT attempt the ford at Upper Slaughter in December - cars can be washed away) and perhaps the two Swells. It sounds trivial, but accurate naming throughout England is important.
By the way, Eastcheap in the City of London has the same derivation from chipping.
Noon is pretty early for Tea, usually taken between 3 and 4.
Above advice about shops closing on Sunday is both true and worth taking notice of. The Tesco in Stow-on-the-Wold is open on Sundays from 10-4.
Advice about not driving after a transatlantic fight is well advised. Especially in December when the roads will be wet so you can't see the markings on the road, it will be mostly dark except for glare, and exhaustion. In the middle of summer I fell asleep in a pub carpark halfway to Stow-on-the-Wold from Gatwick when I thought I could brave it out. At least I had stopped.
At 2:30 in a pub do you expect a full meal (prob with the tainted World Cup you won't need a meal) but normally hot food stops at pubs at 2. Max 2:30. But you'll just be sitting down. Worth checking.
If you intend on driving into Oxford, even to cross town to the particular P&R that you want, be advised that much of the parking has been removed - particularly in Broad Street - and that there is a very expensive Clean Air Zone which must be paid online.
