Hmmm, I recommend just skipping the limit switches. They seemed like a useful thing to me when I first started with a CNC mill but I quickly realized I did not need them and really can't come up with a way I could use them if I had installed them at this point. The reason is that every Gcode you generate in CAM will be setup to zero off of a corner or sides of stock material and so knowing home won't help much. Also with every tool change, z height changes so manual setups are already a given. Maybe one application would be to zero on stock and then move to home and record the offset from zero, providing a handy reference point for when something goes wrong and the original zero references are missing from previous machining. Even then though, a 1-2-3 block mounted to the table would suffice and be more accurate I suspect.