Hello, is it possible to control several receivers with one transmitter ? What about the range ? What speed can we reach if there is a 1 Gbit/s router at the transmitter?

I have been operating an AirGrid M5 HP (previous model) for over 5 years. It is weatherproof (waterproof) and can be installed outdoors.
It is not waterproof..... although I don't think you really mean that. This would mean that you attach the antenna underwater ^^

No, according to our information it is not waterproof.