Is this the right place to be asking this?

1st, Every machine build I have looked at (although I certainly havn't navigated this whole place), uses a screw for the Z-axis. What is the downside to using a rack vs. screw? For a machine that will be traveling with the Z just as much as the X and Y, I would think that the screw would heat up, and just plain wear out.

2nd, Is it possible to use a teaching pendant of sorts along with Mach3? Or is there a way to record the jogging moves with Mach3? I've still got a lot of learning to do with it.

Thanks