I love the planning part too.
If you haven't done London tubes before be aware that some of them mean you have to use several sets of escalators. Lifts should be available but aren't always easy to find. There is a five minute walk from Heathrow terminal 5 to the tube there and a seven minute walk on arrival at Kings Cross. No trollies are available at tube stations to help with your luggage. This might not be an issue for you, but needs to be considered for some. If you have not prepaid you will need pounds sterling. Dollars not acceptable anywhere generally speaking, though a few very touristy areas in London and Edinburgh might at a poor exchange rate. The trams are now working in Edinburgh, at last, hurrah. Have fun and I hope you find out some interesting family history.
