[werk_ag]

A third (or more) Arduino(s) will be necessary only if you plan to re-transmit the signal from the base RX to additional displays.

No, a single Arduino (the one in the RX unit) will do all the work of receiving data from outside weather instruments, process it, do the Davis emulation, feed Cumulus, and then, after processing, broadcast data to all Wireless Display units, that are passive stand alone receivers. The main RX unit is at the same time a receiver and optionally a transmitter.

I have no particular interest on this myself, but I guess taken a bit further this architecture could open new even more complex possibilities for owners. Such has monitoring temperature/humidity (perhaps CO2) on different rooms and returning the data to the base unit. But that would perhaps imply coupling the RX unit with a more robust Arduino model or ideally to a Pi, so as to skip the need for a third computing machine...

I understand what you mean . For now I'm concentrated just in meteorological data, specially data that can be used by Cumulus.