2) When converting viewing angles to obtain the focal length; do you measure the angle between between the extremities of the object and the front lens element or the angle between the object extremities and the sensor plane?
Neither. It is the angle at the nodal point of the lens.
|Black on White by RaVN11|
|Hummingbird and Bee by dibilio57|
from A Big Year - birds
|xheneta iseni _for DPReview by Mike Slade|
from - My Fair Lady - (Portraits in Full Colours Only + A Border)