Hi,
I'm in the same situation as you, designing future house electric system.
Routing all the wires to the main cabinet (fuse box) is overkill since you can not wire a two position switch (in the room) and automation (at the panel) in such a way that they can work together, you either wire them in parallel and then the automation can not turn the light off if the room switch is on, or in series in which case the switch can not turn on the light if the automation failed. The only way to use it would be by using Push-Button like switches (doorbell switches) in parallel with the automation, commanding some type of step relays, but in that case the price is way high for wires and relays.
My approach is to take both light leads to a larger light switch box in the room, plus some 12V rails, there I have some 12v-5v dc-dc reg, Arduino, relay board, pushbuttons and confirmation leds, plus radio. The system's top priority it turning lights on/off, I'm also considering adding another Arduino in ther for the radio communication, just to be sure the main Arduino does not crash and leave me in the dark.
As relays for lights I use the aliexpress cheap relay boards with Songle 220V 10A rated relays, my CFL and LED lights take 200W max, which is under 1A, so the relays should last a long time.
I've chosen the 12V low power buss for the cheap and reliable 12v-5V DC-DC step converters. You may go with 24V if you find the right voltage converters for a good price.
For the sensors I leave the cable tubing out of the wall a few inches, and after painting I cut to the surface level and glue (silicone) a small box that sticks out with holes on top and bottom for better airflow. Heck I even have some dead end cable tubes in the walls for some DS18b20 in wall temperature probes, useful on exterior walls to prevent dew knowing the inside temperature and humidity.
PS. Add some tube to the radiators if you use such things for heating, might be useful for monitoring in/out temps, and correlated to some electric motor ball valves you can have heating zones in your system.
Regards,
Mircea.
