Nice! I've only been to London once when I was 14, and to be honest I don't remember a lot of what I did back then! There is so much to see and do there though, that I am sure you'll find something to your liking. I hope someone else has more valuable input, but wanted to wish you a pleasant trip anyhow! 
Thank you for your wishes, I sure do appreciate it! I thought about since I'm a avid Harry Potter fan, that I would visit some of the filming sites. 
Oh that's great! I think the first five movies were out back when I was in London and I remember we visited Eton College, which is where some of the classroom scenes were filmed, and I remember being amazed by that
However I guess it is a little out of the way, but might be worth combined with a visit to Windsor Castle. I guess you have the chance to see King's Cross, as well as the place where they apparated in the 7th film if you stay within London, plus a couple of scenes I probably don't know about. Great idea!
