If you buy the Iris plug, these instructions show how to add it. As a note, the built in device type handlers from SmartThings work so you don’t need to install the custom code.
I entered pairing mode and plugged in the Iris smart plug, it instantly connected as a ZigBee on/off device (you can go into your IDE and change the DTH to SmartPower Outlet if you want power reporting).
To add the Z-Wave repeater, while in pairing mode, I had to press the button quickly 5 times. This automatically added a Z-Wave device. That device is not controllable through SmartThings (as it is only a repeater) but needs to be paired if you want to use it.