Yes, you need a gateway that connects to Wi-Fi and the Internet. The weather station can be added in the software to add additional management functions. PS: I have a gateway and 7x heads for sale second hand.

I have adjusted the True Temperature on two radiator thermostats by I think 1.5 gad, as these two thermostats are very low to the ground. Now they regulate perfectly.

https://www.netatmo.com/de-ch/energy/modulating-thermostat I found this on the website but haven't tried it myself yet.

Yes, I have. It works, but unfortunately only moderately. The batteries (Varta Power 2100 mAh) have to be replaced about once every 1.5 months because the thermostats do not cope well with the reduced voltage. If they are not under power for a longer period of time, the display may (permanently) freeze. However, the function itself is not restricted by this.

Yes

The scope of delivery includes 1 piece. Thank you for your comment, we have adjusted the system accordingly.

Yes, unfortunately it is absolutely necessary to have a Startpack. Only the Startpack contains a relay that connects to the Internet via WLAN. The thermostats themselves cannot use WLAN, they connect to the relay via radio. It would probably be technically possible to integrate a relay into the weather stations, but whether Netatmo is interested is another question.