I'm in the process of building a Senior.

On Dihedral: The kit instructions result in a dihedral of 6". Based on input from other experienced builder / fliers that love the Senior they recommend knocking it to 1" - 2". Mine is at 2".

On Ailerons: Bob Nelson (the SIG Mfg Senior guru) has recommended that when adding strip ailerons to the back of the existing kit wing add a cap to the existing trailing edge to provide some meat for the aileron hinges. I chose to model my ailerons after the ARF's. This requires re-engineering the rear spar from an upper and lower spar to a single 1" spar as the ARF uses the rear spar as the front of the aileron box for hinging. Also lengthening the wing to a full 80".

Good luck on you mods.