One last question, if I may. I've toured on a solo bike before and generally use four panniers. One thing I am pondering is how to fit gear on a tandem for two people? Any advice from those that have gone before me?
It will depend on whether you are planning on camping and if so, how light you can pack. I've toured comfortably on a tandem when not camping with four panniers. The tour I did when I camped we used four panniers and a Burley Nomad trailer. In retrospect we probably didn't need the second set of panniers or at least not full sized ones.
If you're not planning on camping I think panniers should be enough. If you pack light (I don't) when you camp, panniers may still be enough.
Try a couple of combinations on your 'test' tours and see what works for you.