Re question # 1.
The spoke is the strongest element in the wheel build. An adequately tensioned and "properly fitted" spoke will always outlet the rim spoke bed and/or the hub flange unless it suffers physical damage. Spokes generally fail from fatigue caused by too low spoke tension, improper fit in the flange, or metal defect. In my experience, touring/tandem wheels built from heavier duty components last longer with slightly less than maximum spoke tension and optimal tension balance.
Did you use DT Alpine III for this build? They can be challenge to fit in hubs with smaller spoke holes.
Good luck with you situation!