A good number of the relay configurations will DEactivate when an estop event is detected. You can use an output configured as "OkFaultOut". It will activate once the software boots up and deactivate when reset or estop is activated.
Most small relays will pull <50mA, contactors~100. Total them up and try to keep them under 500mA. You can test with a voltmeter. Measure power supply voltage with nothing other than Acorn connected, then connect the rest and see if the voltage drops more than a few tenths of a volt