I explicitly said that the RPI wasn't suitable... But listed it as an example of a way too powerful device that is still cheap. Just to emphasize that you don't need expensive hardware.

Yes, but the SD card may have a short life if the system writes a lot on it - so far that is the common failure mode of RPi, which are otherwise reliable.

What sort of reliability?

Various smart features should fail safe anyway, if that is true then "reliable enough" doesn't have to be all that high a bar. Of course most people won't put up with rebooting their house once a week, so it isn't that low of a bar either.