1. This is somewhat explained in the game, but technically Legacy locks all the scope scaling to MDV 0% with a base FOV of 65 Hdeg 4:3.
2. With relative your can adjust the coefficient yourself, which is exactly the same as Monitor Distance Vertical (explained in the instructions).
3. Affected will adjust the scopes below 3.25X according to your FOV. With independent they have a locked FOV.
4. You should in most cases not convert directly from ADS to ADS and scopes to scopes. This is because they have different FOV's, so it's better to base all the conversions on a single sensitivity like hipfire.
You can set up the calculator like this, this way both the ADS and ACOG matches your ADS sensitivity, and ADS will be converted to low while ACOG will be converted to high. For MW you have to choose which high and low scope/gun you prefer.