I like the machined lazy susan bearing, as opposed to the cheap stamped ones.
You could use a timing belt for the drive mechanism. With a small drive sprocket and large turret sprocket you would have a dramatic speed reduction & torque increase.
For very large sprockets you don't need teeth completely around the perimeter. Any more than 6 teeth engagement at a time is redundant. Just make sure the sections that don't have teeth have the same radius as the bottom point of the tooth.
Example (of course you would have a hollow hub):
