Regarding balance of carbs, etc I suspect I may have got it wrong. On
reaching JOG my 'spare tyre' was more than somewhat diminished (took
quite a while to regain its former pomp).

Overall I doubt you'll do much better than the old adage: eat before
you're hungry, drink before you're thirsty.

It's what I've been doing on Audax rides.

Off the nutrition topic...

Cornwall and Devon *will* be steep up then steep down, ad infinitum. Do
not underestimate them.

I know Deveon and Cornwall only too well. I had an abortive attempt last
year and was lulled into a false sense of security by Cornwall when I never
had to get off and push. Devon disabused me of my ideas about my fitness.
I very quickly learned that any town on the road map with bridge or ford in
it normally meant a quick descent and a long slow climb out.

Northern Scotland *will* be cold, whatever the season.
(Oh dear. I seem to have laid myself open to accusations of
Southernness, Softiness and Lowlanderness.)

As someone brought up in the north east, parading through Newcastle at Xmas
in sleet and snow wearing a t-shirt was normal behaviour. Besides, I've
acquired an ample layer of insulating blubber since those feckless days :-)