How to measure depends on the use to which the measurement would be put.
Assuming that the use of the measurements will be data for aerodynamic functions:

1. Wing area projected onto a horizontal plane with the chord line at the wing root horizontal.
2., b.
3. The dihedral angle is measured from the horizontal to a line connecting the points 25% of the chord from the leading edges, with the root chord line horizontal.
4., a.

If, for example, you were using the wing area measurement to determine the weight of covering material, or the wetted surface of the wing, then the area would be the developed length of the airfoil surface times the panel length, summed across all panels.

As a practical matter, the differences in definitions, where angles of less than 5 or 6 degrees are involved, will only show up in the third significant figure and can be safely ignored for many purposes. That is the difference between a length and that length times the cosine of an angle less than about five or six degrees.