Questions about Zigbee

Hardware
1

Hey!
Up until now i’ve only used a Tellstick for controlling lights, but i really like the idea of Zigbee, as it’s cheap and used with both Trådfri and Hue.

  1. Is there any point in buying a ZigBee USB Stick in favor of a Trådfri or Hue Gateway and vice versa?

  2. What kind of ZigBee stick/gateway should i buy off of eBay?(Amazon is not available in Scandinavia)

  3. What do i need to read the state of a Trådfri switch/dimmer/motion sensor in HA?

  4. What kind of Zigbee lights/hardware gives the best value for the money?

Thanks! Hope i’m not asking really stupid questions.