First of all, thank you to everyone for sharing some great tinplate videos! Keep them coming!
Scott, I believe the turntable is a pre-war Marklin item. If someone can shed any additional light on it, I would certainly appreciate it.
Tim, I'm not well versed on Hafner sets, although there are others on the forum that may be able to answer your questions about the proper locomotive & tender to go with your cars.
As far as the key movement is concerned, Hafner motors are what I refer to as "Basket Winders". The mainspring is contained inside a four-tab basket, which is connected to the key. The outer end of the mainspring is attached to the basket, so turning the key winds the mainspring from that end. The inner end of the mainspring is attached to a spring hub, which is geared to the wheels in the conventional manner. So, as the motor unwinds, the basket, outer end of the mainspring and key remain stationary, while the inner end of the spring drives the spring hub, gears and drivers. Other windup motors (such as Marx) wind the spring hub, so the key revolves when the motor unwinds. On those motors, the outer end of the mainspring is attached to the frame of the motor instead of a basket.
Starting and stopping the Hafner is easy... I used a string attached to the loco or passenger car to control movement as needed. In shots where only part of the train is shown, I simply used my hand to control it. Sorry to spoil the magic, but that's how it was done! To be fair, most of the time when the locomotive was moving forward, it was doing so with it's own spring power.
Thanks for the videos & comments guys!