this is a great idea, and I love your concept of just going to see things that interest you rather than trying to make it a great boring struggle.
26" wheels with as big a tyre as you can fit. that way it'll be more comfy than anything else.
hydro discs are reliable enough (if you stick to a common shimano unit) these days, and you need the power on a fully loaded tandem!
run tubeless so you can have a lot comfier ride and a lot fewer flats. if you have a problem no big deal, just chuck a tube in there until your next bike shop rolls along
ortlieb back rollers on the front are totally fine if your rack fits it
Interesting thoughts on tubeless, thanks. I don't feel too confident in hydraulics, I have it on my solo bike and it seems so fiddly in case anything goes wrong. I don't like the idea of using anything I can't fix myself.
My thoughts: