Please only use normal relays or contactors for e-stop, SSR's are really only safe for loads like heaters and lamps, i learnt this years ago when i was doing R&D for printing process and finishing machinery. They fail regularly and 99% will fail ON not off. Even when used for heaters you need to use sensors for over-heat which happens when they fail.

If using for motors, always fit a good snubber network to help protect the SSR.

Loving the build BTW;)