charging batteries from the USB port but it gives the power limitations and pin connections you need.
Any load device will draw whatever amount of current it needs from the power source unless the power source just can't deliver it. At that point the output voltage starts dropping off or, if the load current is severe enough, a fuse is blown. You could switch the load on and off but the USB port still has to be able to supply enough current when the load is connected. (Switching the load on and off makes no sense in the context of limit switches though.)
If your limit switches are connected directly to ground, then a series current limiting resistor needs to be installed to limit the current to the 100 ma level (or lower) per load device so as to not overload the USB current output capability.