Floor plan optimization city villa + fill consideration

You should separate router and access point in your mind, then it becomes easier. The router, that is the device you get from the provider, is ideally used only for "dialing in," not for setting up the Wi-Fi. For reasonable Wi-Fi reception, it is recommended to place a so-called Access Point on each floor, that is, a device dedicated solely to offering Wi-Fi. You connect these to your router. As already mentioned, such access points can be easily placed on the ceiling; a network cable as a ceiling outlet is sufficient, since you can also power the APs through it.

So, there are smoke detectors in the rooms and, for example, in the hallway, a smoke detector AND an access point hanging from the ceiling?

and a lamp,
are there already lamps with access point and smoke detector integrated?

So with RM in lamp definitely (not nice) with integrated access point I have seen neither lamp nor smoke detector, let alone both...

edit: Apparently there are lights with integrated repeater...

With us, it will not hang from the ceiling, but on the wall just below the ceiling.

With us, it will not hang from the ceiling, but on the wall just below the ceiling.

That can also be done. However, one should check the datasheet of the access point to see for which mounting position the antennas are optimized.