That's why it is so cumbersome to work with actual apertures. They are not easily determined. Working with f/stops is a lot simpler, in my opinion.

Correct, if both film formats are enlarged to the same print size, the smaller format will have less DoF with the same focal length and f/stop, because it was enlarged more. Remember, we are always assuming the same print viewing distance.

Correct. The angle of view (a) is given by the equation below:

a = 2*arctan(d/2*f)

where ‘d’ is the dimension of the negative-format diagonal and ‘f’ is the focal length.