Hi Andy, welcome to the forum.
I don't have much to add I'm afraid, just didn't want you to think you were being ignored!
On point 3 - You can space the driveside of the BB out a little, though there's not much consensus on how much is acceptable, as long as the non - driveside cup goes in far enough it should be fine. I've used 3mm of spacers to get a perfect Rohloff chainline, I don't notice it being asymmetric.
Also BB lengths can be deceptive, they're not all symmetrical, I can't remember the models but I've had two different lengths with the same chainline! I've seen a list somewhere, but can't remember where. The 73mm shell does make finding the perfect match harder.
How far off complete is the build? Don't forget the photos