Dear Philip,
I’m not really sure I understand your first question (a Figure would help for clarification). Hopefully it is clarifying if I say that projecting the tail-furl axis onto the horizontal plane can be used to define TFrlSkew and TFrlTilt is the angle in a vertical plane from this horizontal line to the tail-furl axis.
I agree with the explanation in your second question.
Modeling a horizontal stabilizer would ideally involve a change to the source code, but in the absence of that, choosing an appropriate TFinBank sounds like the next-best solution.
Regarding the SWRT (Bergey 10-kW turbine), the rotor spins counter-clockwise when looking from upwind to downwind, but FAST can only model rotors that spin clockwise. So, many of the signs of the various inputs and outputs (such as Yaw2Shft) need to be “swapped” to mimic the appropriate effects. See the following forum topic for more information: Coordinate System in FAST.
Hopefully the sun will show itself again. In cloudy places, I’ve heard the term “blue clouds” to describe those rare sunny blue skies 
.
Best regards,