Quite an adventure!
Is this heading to the
Great Divide Mountain Bike Route? (an Adventure Cycling
route).
At least, you'll be on paved roads for a while, and can get your fitness and equipment working.
Here's a link to your
original post in December.
Completely new to tandem-riding; I just got this idea two days ago. Haha. I popped into the town's bike shop today and got a lot more questions answered (the owner was taught on a tandem and is willing to give lessons so yay!).
Your inexpensive
Dawes tandem has a 48/38/28 triple, and a 11-28 7-speed cassette. That 28/28 low gear will make steeper gravel climbs very difficult. I'd stop at a bike store along the way and see if you can get lower gearing.