Mach3 Control Board out of pins to connect to for Homing and limits switches?

[MCmec]

First, I doubt that you could use additional boards as all the boards probably have the same USB address so Mach3 won't be able to distinguish between them.

The standard way to solve this problem is to wire all the limit switches (assuming microswitches) in series. As you will only be moving one axis at a time, if a switch is triggered you know which one it is. Look at the Mach3 manual.

Equally you are only homing one axis at a time (though homing isn't really needed).

So like in the picture and use my free input pin?