Starting off down this road, you can very quickly get bogged down in scenarios. What if you already have house wiring, can you /should you retrofit, can you go all low voltage, what if you aren’t there to fix it? This started to kill the project before it started but with a bit of looking around I have decided the path is full 12VDC.
I have the advantage of having a fresh place to start, rather than retrofitting an existing house. If I was retrofitting though, I would be more looking at LifX and NinjaSphere sort of setup rather than a wired solution. Also, 12VDC LED lighting and arduino communities are making project like this much easier. the amount of actual electronics that I have had to do so far is zero.
Committing to 12VDC is both liberating and restrictive, but then again, so is 240VAC. The main advantages for 12VDC for me is that I have do all the cabling (not electrician), controlling (and programming) using arduino and battery backup without UPS.