~what kind of shaft do i create for spiral stairs? and how do we fit it in right accordingly?
~for stairs in general do i have to specify how many stairs or revit does the calculations alone?
It depends on the design. I would look at pictures online (try houzz) to see how they designed the opening.
You set the maximum riser height and then you can modify in the instant properties if needed the amount of stairs. Revit will modify the riser height accordingly.