I agree on the UI bits. It would obviously require at a minimum, more detail in the preferences pane. One solution for changing modes might be to take control over the device buttons from the main driver, if that's possible -- you could then simply allow the user to assign those as keystrokes for commands, like any other button.

Moving ortho top on world z would act exactly as it does now -- it would zoom, or, more precisely, dolly. Moving ortho top on object z wouldn't have any obvious effect, but if you're in split view, you'd still see what was going on. Perhaps another preference for whether or not you'd like object movement disabled on the projection axis of an ortho view?

For object movement, yes, a lot of it is just showing things around, but it's really very convenient if you're moving assemblies in and out of the way, etc. If you add a rotational snap to go with the current grid snap as an option when doing direct rotation, I think you'd actually get pretty crisp movement -- the dynamics of motion should be exactly the same as dragging. Object snap, likewise, can work in the same way.

/Ella