1. Select a vertex in your model so you are limited to a point, then write down the three normal and three shear stress components.  Enter those numbers into the equation for von-Mises equivalent stress.  Compare that value with the Equivalent Stress result at that vertex that ANSYS computes for you.

2. None.

3. It is recommended to using a range of frequency to span the potential range of inputs to the structure. How is a specific displacement applied to your structure at a specific frequency? A typical input is a harmonic force caused by an unbalanced mass on a rotating shaft.