I dont use a hand held pendant but I use the MPG module to connect a MPG (Hand wheel) , feed and spindle override pots, axis select rotary switch and panel buttons etc. I have that mounted in my control panel (see pic) and I just have a long cable that goes back to the electrical cabinet to connect the MPG module to the main CSMIO.
Regarding the 120v, not sure if that could be used or not, I am not really the person to ask as I dont have any formal electrical/electronics training
Most servo drives have a function in them for brakes, the power is sent to the brake as soon as the drive is enabled and taken away when disabled. If your drives do not have that feature then you most likely could set it up via the CSMIO enable function and use a relay as you are thinking.
Hood