A number of years older than you.
Have been visiting the UK (especially London) since Nixon was in office.
From my POV Fall travel is a great time to visit.
A few thoughts on your itinerary.
Have you driven in the UK? Know about roundabouts?
For many its disarming to drive on the opposite side of the road. I’ve done it a few times and adjusted my mindset quickly. Even did it driving with a clutch. Helps to have learned on one in the days of yore AND to be left handed.
If you are going to drive get ALL the insurance AND get an automatic. Take a paper map. GPS isn’t always that reliable.
On “ back “ roads which can be narrow be prepared for bicyclists, lorries, trekkers with backpacks, dog walkers, cows and sheep! Also hedges can be high blocking peripheral views…slow around corners. Obey the speed limits. IMHO a smaller car is better than a mid size.
Have you considered an easy day trip
by train to the English coast? Somewhere like Whitsable or Brighton. Merely offering something closer to London. Only an 1.5 hours by train to either spot.
Any interest in WW2 sites? Bletchley Park is which is where the code breakers lived and work. Visited in 2021 and spent over 3 hours there. Was surprised I’d be so enthralled. You can take a West Midlands Train from London Euston to Bletchley Park. 45 minute train ride.
If staying in Chipping Campden its a 20 minute drive to Hallies Abby. About the same to the Broadway Way Tower. Have a cream tea or hearty lunch at the Plough Inn at Ford. Definitely check out Fall colors at the Batsford Arboretum.
For my favorite city on the planet check out these links a month before your departure. Might discover sites, events, markets, etc. you never thought of seeing while in London.
The Londonist
https://londonist.com/
WhatsOnStage
https://www.whatsonstage.com/
Secret London
https://secretldn.com/
Ian Visits London
https://www.ianvisits.co.uk/articles/
Dress in layers and make sure your coat/jacket is waterproof.
Check out the National Rail 2 for 1 deal to see if can use it. In 2018 a friend and I traveled from London to Portsmouth by train. Went to see where the series Call the Midwife often films. Upon return to London showed our ticket to the staff in the station office and obtained 2 for 1 vouchers that we used at Westminster Abbey. The available sites change constantly so the Abbey might not be on the list but worth investigating.
https://www.daysoutguide.co.uk/2for1-london
Lastly, Hampton Court is fabulous!