I am working on a trip similar to yours. We are going in Sept of next year so I have lots of time to plan. The working plan now is 5 nights in London, day train to Edinburgh for 3 nights, on to Ireland where we are traveling Northern Ireland for 5 nights and then 2 in Dublin. It is a lot of work, there is so much to see and do, its kind of overwhelming.
I will be watching this thread with interest!