Turning on the gardenlights and the fountain is done with a Sonoff 4ch pro.
A cheap smart switch.
You can add all kinds of smart stuff to GA (Philips hue, Ikea,etc).

Second question; I think you do not need the Google AIY, but I experienced it to be very easy to setup.
And I bought it very cheap secondhand …
But it is possible to build it yourself (google is your friend).

Peter

@Egnos: I think I made something like you want.
I started with the original Google AIY (https://aiyprojects.withgoogle.com/) and made it working (I have the V1 kit).
After that I installed MM on the same SD card.
GA and MM are working seperately.
So I cannot hide modules with GA, but I can ask a lot of questions and GA answers me in my own language.
I can set timers, ask for appointments in my agenda, turn on the gardenlights and the fountain in my garden pond.
I think it would be possible to set the temperature in the house if I had a smart thermostate (maybe next buy).
Playing songs on youtube or spotify: I did not get it working (I think you need the “real” Google home for that.

I am really fond of my Magic Mirror: it turns on and of by a Pir, shows me a lot of personal information and if I say: “Hey Google, goodmorning” it answers: Good morning, Peter, the time is …, the temperature is … it is going to be a cold day, it is not busy on the road to your work, it will take you … minutes, have a nice day … (all in Dutch = my own language).

Finally I build the RPI, AIY with the original speaker and microphone at the back of an old monitor.
I did not use a mirrorglass because my mirror shows thousands of holidaypictures and behind a mirrorglass they were to hard to see clearly in my vision.
So I mounted a plate of clear glass in front of the monitor.

If you need more information, you can mail me.

I hope this will help you with your project!
Peter

Interesting!
Are MM and GA independend or can you influence MM with GA (like showing or hiding modules)?
I think I made my mirror in the same way.
I have the original Google AIY kit in my MM.
They work independend: I can ask Google any kind of questions, set timers and turn on the gardenlights and the fountain in the pond with my voice.
But I cannot hide or show modules with voice.
I am very interested in integrating MM and GA, but I do not know how.
Peter

Thanks; this was what I was looking for!
My first mirror is a kitchen information screen too.
I will try to make this one too (with a personal touch).
Peter

My first MM is running smoothly for a couple of months now (best RPI project I have found on the internet).
Time for a second MM; with a complete different look and feel.
I came across this picture on Pinterest.
Does anybody know who made this miror?
I like it!
Thanks in advance.
Peter

That is exactly what I told you before.
Read the article and you will see how to connect the 3 wires.
And you can change the temperature of the fan to start.
My fan starts at 65 and runs for 30 seconds to cool the cpu.
Peter

https://hackernoon.com/how-to-control-a-fan-to-cool-the-cpu-of-your-raspberrypi-3313b6e7f92c
I use this.
It works fine, even wit a Google AIY Hat on top of the RPI.
I hope it works for you too.
Peter

Same here.
Sometimes it is back for a while.
But most of the time it is gone …
Peter

I have MM and Google assistant running on one rpi.
I used the original Goole AIY kit.
So I do not use MMM-assistant.
I can ask questions and get answers, but it is impossible to hide or show modules.
Peter

Well, I got it working!
MM and Google AIY on one RPI; great!
But I am not a technical person and need help.
Before I placed the AIY Hat, I had a pir connected to GPIO22.
Now the Hat covers all the GPIO pins, I still want to connect the Pir.
Is it possible to connect it to the bottom right connectors (saying GPIO22)?
Thanks for your help!
Peter