How to efficiently search for zigbee / z-wave devices & other newbie questions

I am very confused. I am about to purchase a Raspberry Pi, zigbee & z-wave dongle.

  • How do I efficiently look for cheap and reliable devices? Unfortunately in the “integrations” tab one can only search for Company names and not for applications (example: “door sensor”)

  • Underlying question: If a device is a characterised as zigbee/z-wave, can I be assured that they do not need a hub?

  • Do all zigbee/z-wave devices extend the range of communication? (mesh network) or are there some that do not?

Thanks for the clarifications