Z-wave is working on it’s own wireless frequency.
Depening on your region in the world, it will be a different frequency.
Since your raspberry pi/synology nas cannot communicate wirelessly, you need a z-wave usb key to talk to your hardware.
You do not need both a raspberry pi and a synology nas, one of both is fine.
For Imperihome:
You just need to install the Imperihome service from the Add-ons inside the PulseStation administration panel. If you are on a synology nas, you also need to open the port in your firewall.
Then you just open the imperihome app and follow the instructions as described in our “Frequently asked questions” section.
It’s all very easy.