Better connection schema
At the present time, each device (Thermostat, Valve, sensor) must reach the one and only Internet Bridge in the house. The said Internet Bridge must pair the device, collect data from it and pass the user choices to it via 868MHz radio. Assumed you have a beautiful (and big) house, maybe three or more rooms, you will face the problem: the radio range of IB and devices is very very limited. Under the hood of a marvelous design, you can notice that antenna and radio section are ridiculously small.
You should put some changes on one of two side: whether design, or net architecture.
I think the second way should be better. I figure out more IBs for each house, linked by the wired LAN.
The first IB of the LAN becomes "the master", and should work as usual, with just a minimal difference: should you put it in "pairing mode", it will open two ports on the LAN, i.e. 5004 and 5005, and listen from them.
Each further IB, at the moment it starts up, before searching for Tado cloud, it should search locally on the LAN for a IB server on port 5004. If it exists, this further IB puts himself in "slave mode", functionally a bridge between radio devices and the main IB. It can pair the devices in his neighborhood, then it replies the inputs to the master.
I think this way it could be simple and reliable.