Number of RJ-45 sockets "network sockets" - What makes sense?

You don't have to demonize Wi-Fi. However, please use cables where high data volumes are frequently expected. I consider the refrigerator etc. dispensable, and an audio stream is in my opinion not an issue that must be tackled with cables. Plan one access point per floor, so lay cables on the ceiling.

Well - it's probably like with many things... For those who only consume apps and browse, Wi-Fi is enough.

But once the 500 holiday photos need to be viewed, edited, and saved, Wi-Fi is too slow. Videos, good night. And when the kids want to play games, they'll give dad a hard time about Wi-Fi and ping and so on. And how many times in my life I've heard "The Wi-Fi isn't working," "Restart this and that," and "XY has no connection"... That doesn't happen with cable. (Unless the cat has unplugged it again...)

Of course, there is now really good, fast Wi-Fi hardware. But it not only costs more than cable, it is also less secure and depends on updates. And the faster and higher frequency, the stronger the attenuation through walls, the more APs I need.

So no. Wi-Fi is for devices that fit in pockets or at most handbags. For work devices, you need cable.

Exactly what Alex85 described. Use cable where bandwidth is needed, otherwise WLAN is sufficient. In video editing, IMHO it doesn't matter whether it's over cable or WLAN, I would never think of doing serious video editing on a network drive... but that's probably the use case for very few. And I wouldn't transfer the 32 GB SD card with pictures over the network either, but would copy it directly to the NAS - regardless of whether WLAN or cable. But that's probably more a personal preference...

Since a decent NAS is as fast as an internal drive, you can definitely do that... Of course, it works a bit better on the built-in SSD... luxury problems. And the photos from the memory card definitely go over the network to the NAS. First, I don’t want to walk to another room (that’s the whole point of LAN...) and second, the card + card reader first have to deliver more than the network can. And that rarely happens. Besides, I don’t want to put them somewhere, but directly into the right folder.

Where does it make sense? Ever connected a LAN cable to an iPad or something like that?
If already FTTH (like with us), then also install a few double sockets.
The future will be, nobody knows, but I suspect WLAN or radio. LTE/5G can already do a lot.
Back and forth – it makes sense to have 2 double sockets at the TV, just like in the study, if available. Printer with LAN and a NAS or laptop too – and the sockets are occupied.
We have TV 2DS, next to the TV wall in the living/dining room another 1DS, in the hallway 1DS, in the upper floor hallway 1DS and in the study 2DS. They all come together in the basement next to the fiber optic cable, patch panel, switch, router. Our phone also runs over the network cables (just over 2 or 4 wires). WLAN on the ground floor, thanks to the wooden house and mimo, even with the notebook good data rates.
For cameras, it still makes the most sense to use LAN with PoE.

Does the electrician also lay the cables in such a way that they can be pulled out of the conduits again

Conduits, good keyword. I would say,

In the end, 18 Cat 7 cables arrive in the basement and are laid on the patch panel

minus the planned four connections results in fourteen conduits - that sounds like a realistic dimension

I would now directly distribute from the basement and would put the Fritzbox there. You don't have to access it that often anyway, so you can also go to the basement. Additionally, I would install a double socket in every basement room,

That might mean one more WLAN access point than if the Fritzbox were in the living room, but basically your network architecture is the more correct one. The brain belongs without detours at a starting point.

We are having the same discussion about the topic of sockets

That is a significant reason for me why I could go from tenant to builder: to create something that wipes all provisory solutions and compromises off the table, or put more briefly: no more extension cords ever, all sockets in the wall.