advice sought regarding the selection of a milling machine vise for a small milll

I have an Elgin knee mill with an 18" table. Although small, it's built like a tank. It is fully manual. It's time to equip it with a vise and turn it on. As I studied the selections, I saw the at least two different manufacturers offer a "drill press vise" with stepped jaws. It seems to me that stepped jaws would be a great feature to have on a "milling machine vise", especially when working with thinner material or using the mill to drill a hole though a work piece. I recently used this feature of an 8" Wilton and it proved to be very convenient.

Question 1: should a milling machine vise have stepped jaws?

Question 2: is there some concrete difference between a so called "drill press vise" and a "milling machine vise" ?

Question 3: is a rotary base a must have feature or should I buy a vise that can accept a rotary base later?

Thanks in advance