In the middle of the staircase landing, a socket with LED lighting. That’s enough to softly illuminate the entire hallway without having to turn on the lights all the time. Especially at night, when you need to go to the bathroom, it's super comfortable. I’m missing a LAN port in the study or the bedroom because you said the names should be different. I wouldn’t save on those 150€. Or has watching TV always been taboo for you? A LAN socket for an access point is missing. It would look good on the left wall of the HKV. Relatively central, and you can place a cabinet in front of it. Or behind the doors in the guest room or the study. Maybe also a TV connection for the guest room? Do you like floor lamps? Then have switchable sockets installed.