in moste cases (of old HDD's) you just have to put the power on the complete HDD. it runs on 12V and has a simple connector. That's huch more easyer than making your own controller.
Sure, if you can find a way to feed 'em three phase electricity, probably via an "H" bridge style thing.
I did not know that any of the motors were AC.
Yup, lots of people keep the hdd motherboard intact because you can often short a pin or three to force the drive into 'always on' mode.