I just noticed the ad for the Mercian says it has a 6-speed freewheel. Not that there's anything particularly wrong with that, but you might want to ask what the gearing is front and rear to make sure it spans a good range for touring and has enough in-between gears to be useful.

I don't know what size (width) chains are used with 6-speed freewheels (SK, would you or Bubba know?). If it's the same size chain that's used w. 7-8 speed then you're OK, but if it's an oddball chain width then you might want to think twice.

You could probably upgrade it to a 7- or 8-speed cassette but that would involve having someone who knows how to do it stretch apart the frame at the rear dropouts a few mm wider to accomodate the wider hubs that a 7- to 8- speed would require. And you'd need a new wheel w. the new wider hub and cassette.

Which is all entirely do-able but possibly not in the time frame you have.