I'm thinking about a similar project. One thing I'm struggling with is how to detect the current relay status. You will not notice when another push button is used, so your MySensors device in your controller will only switch between on and off without any meaning to the physical relay on/off. Maybe it is possible to use a mosfet with the 24v relay connected as gate to sense a switch-event triggered by any push button to update the status of your light. Just an idea at the moment, maybe someone with more knowledge on electronics can form a curcuit out of that.