Dave:

Be aware that tire wear - especially rear tire wear - increases very rapidly with higher vehicle speeds and higher laden vehicle weights. You will probably be doing a fair amount of highway riding (e.g. 50 MPH or more, far faster than usual city riding), and your scooter will likely be as heavily laden as it has ever been. So, if you have the slightest doubt about that rear tire, replace it now. It is a PITA to replace tires while on tour, you have to wait for the shop to procure the new tire, you have to find a shop familiar with your scooter, etc.

Trying to get the last 1,000 or 1,500 miles out of the existing rear tire is just 'not good economics' in this context. FWIW, I replace the tires on my ST 1100 prior to beginning any long tour if I have the slightest doubt that they might not last all the way through the tour. It doesn't matter if the tires have 40% tread wear remaining - if it won't last for the planned tour, they get replaced.

You don't want to be out there trying to enjoy yourself and at the same time being constantly worried about whether a part (tire) will hold up.

Get the service done early enough to permit you to put 100 miles or so on the scooter before you head out on the trip. That will be sufficient use to determine if there are any minor headaches present arising from the service visit (e.g. something that might need a further adjustment).

My experience with UK ferries is that they price their sailings very much like the airlines. If you book well ahead of time for specific sailings, you can get very low prices. If you just show up and buy a ticket, you pay "full list price", which can be outrageous. The ferry companies don't make any distinction between a small scooter and a huge Gold Wing or Harley-Davidson... they are all motorcycles. I suggest you do some research. One alternative might be to book and pay ahead for a 7 day trip, and find out what the change fee and/or price increase is if you decide to prolong your voyage for a few extra days.

Michael