Does the IMAX have assigned seating?

Yes

Yes but when you buy your tickets you get to choose your seats out of the available seating.

Yes, the seats are assigned, but you can see which seats have been taken and choose which seats you want to have from what's available.

Yup it sure does, and you choose your seats. The regular auditorium's do not, however that could always change I the future. I will say though, when ordering online or through the the seating arrangement is not aligned with the screen. If you're looking for center, it's between seats 12-16 on most of the rows.