Where are you travelling from to get to Dover? If you're flying in to London, I would do a 'pre-cruise' arrangement with one of the two hotels Carnival has agreements with. You can book them through Carnival and arrange transfer to the pier at the same time. I will be on this same cruise and that is what we are doing. We will have 6 people in our party and it just makes sense to do it (for us anyway). We cruised out of Rome Sept 07 and we did the same thing then.
Regarding the excursions, we haven't decided exactly what we're going to do but I know it will be fun! This will be my 5th cruise with Carnival and my husband's 4th. We are so looking forward to this!
Have fun!