Hey Mario,
I came up with a similar solution back in June which is working great --- posted here. - https://www.raspberrypi.org/forums/view ... 7#p1482843
The small difference between yours and mine is, I didn't splice the power cable and I did use the timer relay to just briefly trigger the GPIO Low to cause the wake up function built in the Pi. For ShutDown I setup Kodi's power save feature, which will shutdown the pi/kodi when left inactive for whatever time you set.
With your setup you risk corrupting the memory card Image due to the risk of cutting the power before shutting down correctly. ( its way to easy to just power off your TV before shutting down the Pi )
Take a look at my post
J03