Hi Cory
In Ports & Pins, Spindle Setup, M3 turns spindle ON, Output 2, You could use it to turn on both spindle & Dust Skirt, M5 at end of G-code will turn them off.
Then in Ports & Pins, Outputs, assign Output# 2, Printer Port it's Port 1, Pin's 2-9, 1, 14, 16, 17 to standalone plc input.
For ModBus it's Port 0, then use Brains.
Look at modbus and braines section for examples.
Maybe a starting point, Not sure which way you want to go.
Hope this Helps, Chip