2. You have to try it out, I can just about manage three floors with the lift in the stairwell.

1. always in the centre of the room. Make sure that the air in the room can flow around the sensor. Not in a corner, shelf or the like. It should not be above radiators or near windows. To measure the perceived room climate, I would place the sensor about 140 cm above the floor.

2. it works for me over 3 floors (hub in the middle of the basement and sensor in a corner on the 1st floor), distance approx. 10m through walls and floors. I would recommend you start with one hub and install it centrally in the middle of the house. If necessary, you could add a second hub to the network. As Legi1 wrote, the repeater function is only active with mains-operated devices, e.g. lights with integrated ZigBee receivers. From the description in the app: "The reaction distance indoors is about 10 m (walls are permissible); outdoors the reaction distance is about 65 m."

In principle, the 10m is correct, but remember that all sensors and actuators in the ZigBee network build up a mesh and pass the signals on to each other, so in principle the distance to the next related ZigBee component must be ≤10m.