So I've found a buddy to come along with me and we've worked out the countries that we're for sure going to visit.
Starting in London (airfare is the cheapest..) then to the north of france, the netherlands, germany, czech republic, austria, switzerland, italy, south of france, spain (hopefully seeing the running of the bulls, and then to Ibiza), west of france, and back to london.
We still need to decide the specific sites and cities we want to visit, but that's our route.