associate a mini OpenWrt router, self powered and an Arduino.
OpenWrt router and Arduino are known to be low consumption tools.
OpenWrt on TP-LINK TL-MR10U
OpenWrt on Ext Root
Arduino plugged in OpenWrt
OpenWrt & Arduino
Larger load relays could switch domestic power (230v DC) with a small voltage as source (5v of Arduino).
Arduino have some in/out availables but Arduino ethernet or Arduino UNO with ethernet shield use somes to communicate.
The idea is to use a shift register (74HC595), to drive up to 8 contacts via load relays per register for only three arduino ports. Note that several shift registers could be bring together.
Timer for small duration task is draft.
Talk to Arduino works with arduino GUI serial monitor open but not if closed ... :(
Arduino Serial with Shift Register sketch (as draft): Old stuff