Which router for our new building?

I do not mean operating in the sense of typing on the keyboard, but in the sense of providing the switch’s services.

I understood, therefore I subtract the connection from the basic requirement of the needed switch ports, as it is a stand-alone device.

That is why you should design your network so that on the one hand you don’t oversize anything and think in terms of active and passive end devices to be operated, but on the other hand also avoid configuring segments in such a way that it creates additional interconnect requirements. This is not a DIY field ;-)

So concretely: 2 switches, 1x16 non-PoE and 1x4 PoE (then lying on the floor in the 19" rack)?

So specifically: 2 switches, 1x16 non-PoE and 1x4 PoE (then lying on the floor in the 19" rack)?

Maybe.

I would look at the power consumption on the datasheet. Then compare that with a 24-port PoE switch. There are also ones where only some of the ports support PoE.

I would look at the power consumption in the datasheet. Then compare that with a 24-port PoE switch.

In the datasheets, as far as I have seen, only the max. power output is described. I have learned that there is a "base consumption," which is correspondingly higher in larger PoE switches because the power supply is bigger.

There are also some where only part of the ports support PoE.

that is my 3rd alternative

Then do a quick Google search. For common devices, you can find values in forums.

So far, two 16-port switches would be sufficient...

and that would be 16 patch ports, but only six switch ports.

Or five 8-port switches! Or eight 5-port switches! And then one more for aggregation. Or better yet, all in series? As I said, thinking about which port is currently patched is nonsense. Then one small power supply per switch each, and the losses add up.

In my configuration, 40 of 52 ports on the switch are permanently occupied. Starting some hack job just because of the 10 mostly unused room connections is unlikely to spark much debate.

In my configuration, 40 out of 52 ports on the switch are permanently occupied.

If so many devices are active, that is completely legitimate. You would go crazy constantly plugging and unplugging.

My configuration is the complete opposite. A handful of occupied ports, and that might change in 2 years when the oldest gets a PC. Then I will patch this one cable into a free port on the 8-port switch. Also completely legitimate.