re: UK trip

You can spend several days in London alone and not run out of great places to see and experience. Then there are day trips to areas near there like the Cotswalds, Greenwich, Oxford, Bath, Windsor Castle, etc. I've been 4 times and haven't nearly run out of things to see/do in that area.

I might dial the trip back to just England, Wales and Scotland, leaving Ireland for its own trip. Then spend 2 weeks if you can. More would be better to truly experience the places, as you say. For that, I feel like you need time to settle down in some places for a few days and experience living there beyond racing from museum to historic site.

The Brits take much more and longer vacations than Americans. One who just got back from a long trip to South Africa told me that he feels you can't really enjoy a place until you've spent "at least a fortnight" there. I laughed and told him that most Americans will never in their lives take a vacation that long.