Home location on CNC Lathe

To be honest, it doesn't really matter where Z home is. You can't rely on limits to avoid mashing the tool into the chuck anyway. (consider long boring bars....)
However, if you fitted a hard-stop for the tailstock, perhaps that would help with repeatability on occasions when you leave work in the machine with it powered down.

On my Schaublin, there are hal sensors for home/limits. The X is near max +X, and the Z is near max +Z.

I have set the all axis homing to first home X and then Z. I set my home speeds pretty slow. It is up to me to be sure the tailstock is pushed to the back end of the bed, and to ensure there is no tool like a boring bar mounted which would wipe out on the spindle during that first X move.

I haven't got my ATC working yet, but the whole concept of a safe tool change position on a bed type CNC lathe with tail stock and old rotating turret ATC seems aspirational at best.