molahs:
The final unit will be ATTiny84, RF2401 with 5V to 220V solid state relay (unless I can find a better way to switch the 220V) and battery.
I personally wouldn't bother unless there was a retrofitable device that would replace the existing light switch. It should have a switch that I can manually press to turn the lights on and off and also responds to an RF signal to turn the lights on and off