That's an awesome list of walking routes, not sure how many would fit your criteria of "mini expedition" though: for example the South West Coast path is about 650 miles, most of which are pretty steep, definitely not something I'd want to tackle in any kind of "bushcraft" style.
How much time do you have to devote to the trip?
I was thinking 5 days to a week, but I do have a pretty flexible job at the moment so I could take more or less time off.
I figure that even if I don't do a whole route, I can still pick up pieces of it here and there. I tend to be more about the
journey (the walking) than the destination (being able to say I did the whole route).