Number of network sockets; how to plan Wi-Fi in the new building?

Or you can make a small adapter ring between the access point and the ceiling. You can hide the cables in it. Someone posted a photo just a few weeks ago. It looked quite OK.

Where would you place the access point? The access point does not belong directly in the corner of the wall. Centered placement simply has the best WLAN radiation.

Correct.
But if you are not building a completely convoluted mega palace, the central positioning is simply not necessary. 10m through two walls is no challenge, for example, for the mentioned Ubiquiti APs. Therefore, I would not neglect the aesthetics and rather hide the APs. Also place the one on the ground floor a bit towards the terrace/garden.

Good thing you mention it. It wasn’t quite clear to me so far why you need a keystone module and can’t just mount an RJ45 adapter?

Because a normal RJ45 plug is not practical to crimp onto a fixed cable. A field-installable connector, on the other hand, fits poorly in the tight conditions at the access point. The rigid cable does not exactly increase this pleasure.

Those are repeaters to me, but fine. Let’s establish: every access point gets its own cable connection.

Repeaters are basically amplifiers. They receive the signal from the client or AP and duplicate it in the same wireless network.
That means every data packet passes twice through the WLAN. From client to repeater, from repeater to access point.
This halves the bandwidth of the entire WLAN.

That is why access points are cabled.
If that is not possible, you can use mesh. In mesh WLAN, the access points communicate among themselves via a separate wireless network. The bandwidth of the WLAN where the clients are located is then not halved.

But yes, mesh also promises smoother roaming. That is presumably what you expect or what you are referring to.
The involved APs also negotiate who can best serve the client and hand the client over. Although I consider this unnecessary in a single-family house where one access point is on the ground floor and one on the upper floor, with reinforced concrete in between. The client is smart enough for that since the transmission powers of the two APs are significantly different depending on which floor the client is on.

The client is smart enough for this since the transmit powers of the two APs differ significantly depending on which floor the client is on.

That did not work in our current house. The phones clung to the registered access point even when hardly any data was flowing, although a better reception would have been possible from the hallway on the 2nd floor. Only after a complete drop did they register on the 2nd access point. Since we installed 2 Unify access points with "roaming," it has worked flawlessly on all floors.

The seamless roaming function in unifi still does not work well or causes more problems. You probably have not activated it either. The client controls it. Therefore, set the transmission power accordingly for each Wifi and access point, and roaming will work smoothly.

Before that, I had other access points; with Unify, it has worked from the start. With all the possible functions, I find the Unify very confusing to set up if you only need standard things for a private home. You can clearly tell that they were made for a different market.

I would go with the NonoHD today.

Why Nano and not the AC-Pro?