Which sensors for what? Inspiration

that everything should be done with bus cable if possible (4 cores?)

For KNX, you don’t need bus cable to the consumers since the actuators (at least when installed new) are located in the distribution board. It is important to run a separate phase (L) conductor from the switch cabinet to as many consumers (including sockets) as possible (you need 2 anyway for shading). This allows you to retrofit actuators later if the initial investment should not be too high (e.g. dimmer actuators later, etc.). Bus cables must be laid at all points where you want sensors (switches, temperature controllers, presence detectors, ...).

Maybe I'm talking nonsense now (and have to read it again) but wasn't there the possibility to use cables with more or fewer cores depending on the application, all of which can serve as a bus? Maybe I'm mixing something up... as I said, the electrical part is not really my forte...

Well, to avoid laying a 3-core cable (L, N, PE) to every consumer, you can use 5- or 7-core cables. These then have 2 or 5 phases (L) and "share" the N and PE conductors. With a 7-core cable, 5 consumers (lights, sockets) can be supplied and switched separately. However, for shading (direction-dependent), you need 2 phases. The KNX bus has 30V direct current. Some sensors require power supply, some get power via the bus. Black and red are the bus, and yellow and gray are the power supply (illogical to me, but whatever). That is why the typical KNX cable is 4-core.

I would have liked to have the smart switches too, but now I have 4 pcs. 4-gang rocker switch at the living room door.

Wow 16 buttons.

1. How do you implement things with photoelectric sensors?

Simply use standard photoelectric sensors. Preferably with a 30V operating voltage so you can power them with the second pair of wires from the bus cable. The switching output goes to a binary input. You figure out the logic yourself.

This is what my mailbox looks like, for example. Of course, it also works with two magnetic contacts but I found the photoelectric sensors more accurate since it only reports mail when there actually is something inside.

2. How, tell me again, do you do it with the pot roast?

Just use a bit of imagination. Temperatures are reported on the bus and a logic triggers the corresponding light effects accordingly. You can also monitor the times in addition. With KNX, this is a piece of cake. It’s really very specific but some people need it. I know someone else who gets push notifications with the measured values from the meat. Everyone has their own quirk and then occasionally goes wild with it.

basically I should make sure that as much as possible is installed with bus cable (4 wires?) so that we are as flexible as possible in the end? Can you control everything with it at the end? Also lights, shading, etc.?

Yes, that’s how you should do it. Lay the bus cable everywhere you can. I write that all the time and always get opinions that it’s unnecessary. But that is not the case. Because later you end up needing the cable as RomeoZwo proves with his awning.

With KNX you don’t need bus cable to the consumers, since the actuators (at least if you do it new) are in the distribution cabinet. It would be important to run a dedicated phase (L) conductor from the distribution cabinet to as many consumers as possible (including sockets) (For shading you need 2 anyway). You can also retrofit actuators later, for example,

Well, as just said, if the bus cable had been laid everywhere then the awning would have been connected in no time. (Rollotube X-Line)

but wasn’t there the possibility to use cables with more or fewer wires depending on the application purpose, all of which can serve as bus?
Maybe I’m mixing something up... as I said, the electrical part is not exactly my strong suit...

As bus cable you should use the freely available J-Y(St)Y 2x2x0.8. At that price you can’t complain and it is approved for all bus applications. Surely you could also repurpose CAT or DMX etc. but why should you do that? If there is no other way I would consider it, but in new buildings just lay the green cable everywhere and that’s it. Then you’ll use 3-4-5 rolls, whatever, the ~35€ per roll really doesn’t matter. You have to lay the NYM cable anyway and the green cable next to it doesn’t bother at all.

Where you really plan only sensors (PM, switches etc.) the green cable is of course sufficient as RomeoZwo already said.

They then have 2 or 5 phases (L) and share N and PE conductors.

... as long as the 3-5 phases are protected together and thus the overload of N is avoided or N is properly dimensioned.

Black and red are the bus, and yellow and gray the power supply (illogical to me, but whatever). That’s why the typical KNX cable is 4-core.

Bus as well as power supply from the KNX power supply run over black/red. That means in most cases a bus participant is connected only with these two wires. White/yellow could be powered separately with low voltage via an additional power supply, but this is not mandatory.

Well, as just said, if the bus cable had been laid everywhere, the awning would have been connected in no time. (Rollotube X-Line)

If the awning had its own phase (L) in the control cabinet, it would be connected even faster to free outputs of the 20-channel switching actuator. But yes, a bus cable there would also help. By the way, the WMS UP transmitter has been ordered.