I like the chain cause on its side its only a stud tall is it doesnt force you to build a hug platform. And i like the worm gear because although its simple it puts alot less stress on a motor. I would also suggest that you use a friction gear (https://www.bricklink.com/v2/catalog/catalogitem.page?P=60c01) on the chain part to prevent damage to the chain as a worm drive is not movable from the gear end. This would let you rotate the carousel for positioning purposes.