I'm adding e-stop like features for the printer at work. I would personally avoid a software controlled e-stop unless it was on a dedicated safety controller. These tend to be not cheap and often come with there own perculiar programming methods.
I've chosen to split my power supply 3 ways. 5V psu for duet. 24v psu for fans (think fan stopping on a hot hot end) and 24v for the steppers and hot bits. I've a relay (actually a pair of force guided relays, but thats probably overkill for your intention) whose coil is grounded by the duet PSU on pin and fed by a non-latching push button initialy and then by spare poles on the relay once the relay is energised. The relay cuts the mains to the stepper/hot bits psu. All contacts are protected by fuses to minimise the chance of contact welding. In use the duet needs to be on and M80 command sent then the reset button will arm the more dangerous parts of the system. I hope to setup the duet to drop the PSU on signal on heater fault. The user would need to visit the macjine to restart. That is intentional as an e-stop implies something went badly wrong and things should be checked over.
If you are however just want a convenient stop process button, rather than an emergency stop then my ramblings are irrelevant!
