To comment on the bicycle itself, the 2 chain thing is cool. I don’t exactly know how it works, but I have already seen retro-direct setups (1 chain + 2 freewheels, with-or-without a jockey wheel) and it is something that has interested me. The big difference here is that with retro-direct, you keep pedalling backwards for the other gear.

I imagine retro-direct could be done with 2 chains for the redundancy, perhaps even with different types of drives for each (like some cheap geared belt for the low gear, normal chain for high gear). Though this would be more suitable if swapping out gear combo was not too difficult, to adjust to rider fitness.

EDIT: I should say with chain vs belt I mean whichever gear you expect to require the most force which may in fact depend on cargo weight+hills. Though the chain being the smaller one might just be smart to reduce wear (esp. w/fully enclosed chain case, exposed belt).