Hi Doomsayer19

I haven't done a short campaign but think the following is correct:

The number of turns is dependant on how long it takes you to fulfill the short campaign victory conditions. I believe you can then continue past that if you wish.

Unlike in MTW you start the short campaign at the beginning with non-advanced units just as you would do in the long campaign. This is different to MTW where you had early, high and late periods with different types of advanced units at each period.

Hope this helps.