Sounds like a great trip!! I'm not sure that you can get suites or Castle Club on DVC points, but you could certainly ask. You also may be able to request an upgrade for additional cash when you check in. The VIP fastpasses would be great, but I'm not sure that they are really necessary in June. We went to DLRP in late June/early July a few years ago, and found that the parks really were not very crowded. By using the regular fastpass, we were able to do everything we wanted with minimal waits.
We also took the Eurostar once from London to DLRP, and my kids really loved it! It was the highlight of the trip.
We will be on the same cruise with you, but will not do DLRP this time, because we were there only a year ago. We will probably do London pre-cruise, although I am thinking about getting outside of London to see more of England. Don't really want to rent a car, though, so I'm not sure where we would go.
Have fun planning!