@AntoZ 

Hi, Thank you very much for your time and patience.

"For both locations I would setup two internet connections: one terrestrial (xDsl) and one mobile 4G."

- Do you need to plug the xDSL cable and 4G SIM card directly into the Deco? or Was there already a DSL/4G gateway/modem?

- Do you plan to use both connections spontaneously, or one as primary and the one as Backup connection? 

-For the VPN connection between two houses, can you give me an example of what you wish to achieve through the VPN tunnels?

It would be very helpful if you could add more details so that we could narrow down the choices.

Thanks again and best regards.

  @David-TP 

Q>  Do you need to plug the xDSL cable and 4G SIM card directly into the Deco? or Was there already a DSL/4G gateway/modem?
A<   For the DSL network the connection is Ethernet directly to the ISP gateway.
        Instead for the 4G I would like to use a DECO.

Q> Do you plan to use both connections spontaneously, or one as primary and the one as Backup connection.
A< I would use both connections spontaneously ... as my experience "tells me" that when I need the backup the fail-over connection does not work.

Q> For the VPN connection between two houses, can you give me an example of what you wish to achieve through the VPN tunnels?
A<  For my smart home I use Sonoff and Eufy security products / devices
Both manufacturers have smart scene tasks that require devices reachable on LAN.
Eufy example: if "House 1 CAM "A"" detect a human, do sound (siren) on both homes and record to "House 2 network HDD""
Sonoff example: I have the the Sonoff  "iHost" (A local private server for houses). IHost need to reach the endpoints on LAN.The feature is called "LAN control"