Roatation
I never put a used tire on the front.I prefer to leave a new front alone until it gets old or some other reason to replace it.I may wear out 2-3 rears before the front goes away.
I've had some fronts go flat rapidly on the tandem and its not pretty.We didn't go down,but came close.We were going about 18 on a straight/level surface and it was as if we hit ice.
As for tubes,I would not use anything marked lightweight.Other than that,I think tubes is tubes.
dan