George(?),
Thank you for the advice. Yes indeed, the bike would be with Rohloff. I was considering that SJS would build the wheels as part of a shipment with many of the other components, and the frame/fork would be a separate shipment. Such an arrangement would result in a much lower cost. They may however balk at such a tedious arrangement.
A dynohub is a matter of high uncertainty that I continue to wrestle with. We tend to shun electronics while on tour and find that an extra battery and charging around camp are sufficient. However, I see benefits and if we want one, now is the time. Eventually upon retirement, when we have more time to tour in more distant unfamiliar lands, it may be that constant GPS access is desirable and so a more pressing need for power on board.
I am sure that SJS would be happy to put wheels in one box (on one invoice) and a frame and fork in another box (with a different invoice). My Nomad frame in 2013 with some other parts in the box cost 118 pounds for shipping and packing, I am sure a tandem frame would cost more for shipping than my solo bike frame.
This past spring I got a much smaller box with parts from SJS, this box was smaller than the box you would use for a wheel, the shipping cost was 35 pounds.
I do not know what triggers a customs fee since most of my shipments from Europe were free of duty fees. If you have to pay duty on a box with two wheels, one of the wheels has a Rohloff on it, a good amount of your savings may dissipate. My point is that you may save on customs fees but you will pay more for shipping with multiple boxes.
As mentioned by others, there could be a warranty difference between complete bike and a frame, but that is something I never looked into.
I have never even ridden a tandem, I have no advice at all on that.
If you would never use a dynohub, then it would be unnecessary. I run battery powered taillights on my dynohub fitted bikes because I want to be able to use a flashing taillight while I am using the hub for charging purposes. I have heard that one company makes a dyno powered flashing taillight, but I have not seen one, All the dyno powered taillights I have seem do not flash, thus my preference for battery powered taillights.