Looks like over-kill to me, but...
Test cable runs first and be wary of running 12 near 240 (they should NOT share the same conduit) crossing at 90deg is preferable.
Everything here is 230 Volts. I don't want that anymore.
If i make it 12 Volt i save energy and can power it one day with photo voltaic.
If you come to sell your house, will this effect the price? Will you want the availability of mains in the future.
If you have a ring main for the lighting, can you use the existing switch wires and place your 12V controllers above the lights, so effectively re-using the cables and not worrying about sending 12 over long distances? This would allow you to revert to 240V at any stage.