I agree with Steve. It's fraught with danger for a beginner messing with mains electricity.
However, that said, as an excercise.....
That's a current sensor, if no current drawn what then?
No, better to use Steves suggestion to use a mains powered changeover relay in your circuit and when power cut, use the contacts to do whatever you want.
I'm assuming a seperate DC(?) supply for the other relay(s) you mention.
I can understand your need to be notified but how? Email, text or whatever.
Each needs a hardware method. If power cut do you lose internet when the router shuts off for instance, so no wifi or email.
To text requires a mobile connection and SIM module.
Semaphore signalling requires a man with flags....with all the attendant beer and food problems 