Focus would be handled by the camera, although I might be inclined to say that the use of a camera in MF
mode might produce better results than one in AF
mode.
The head movements and the shutter release would be handled by this device. I would expect that head movements include both pan and vertical movements.
I'm not sure that the Hassy would give you less images. The key to that equation would be the field of view presented by the camera, and given that for any camera, a "normal" FoV is always expressed in terms of the FoV that our eyes present to us. Thus a 50mm lens is considered norm for a 35mm camera, 80m for a 6x6, and so on.
PHD cameras have smaller sensors and shorter lenses, but most things relating to the FoV are still expressed as in terms of a comparison with a 50mm lens on a 35mm camera, and thus by reference, with the human eye.
Thus, while the Hassy should present individual images of far greater quality and resolution, the underlying fields of view should be similar, and thus the number of images needed should also be somewhat similar.