Typically, that contactor would be used to cut power to the entire system which means it needs to be able to handle the entire load of the system. Are you sure that 25A is rated high enough to do so?
If you pass that test, I would hook it up as follows:
1. Use a common 120V neutral line.
2. Place the contactor inline between the "system power" indicator light and the control module.
3. Hook up your incoming 220V hot legs in line to that box on the far bottom right of your diagram.
*This assumes your estop button is NC and, is a twist style that remains open once pressed until twist reset.