Not sure you can get 100% of number 3 and I do not think any part of #3 alone would be tied to HE.
You can set up music in a Google routine. But, I think it is only one.
As to using switches, you could trigger the entire routine from an HE switch (virtual or other). But, they have limitations. I have yet to figure out how to trigger a Google home routine that doesn't include a greeting along with it. It won't let me save the routine unless I accept access to private data and that triggers the greeting.
This is the one and only use case where I use Alexa (on a Bose smart speaker)
I'm fine with the greeting... Although it's my account and I'd love for it to say any other name.
The routines Ive had in place since the kid was born, so it's not new. I just want to switch control over but also not allow the kid to use voice commands cuz.... That could be trouble.
Today I have everything set up how I want... Ikea button is pushed and HE triggers the virtual button in google home to start the routine. Tomorrow I have to figure out how to make the button never work again after it's pushed once (until night time)
Use a private boolean. In your rule set a required expression of boolean=true. Have an action in the rule to set boolean to false when it runs, then make another rule to set the boolean back to true when mode changes to Night. Examples below.
Make sure it's a household routine, personal routines don't allow Hubitat switches as triggers. Apart from that I'm stumped, mine are working fine still.
Did you get this working in the end? I can't see any hubitat devices in the trigger section of automations, only Google homes and Chromecasts. I'm using the community GH integration, and all devices are in rooms (GH rooms and hubitat rooms)... and yes it's a household routine.
Once you add them to the google integration go into the google home app and add them to your home and then to rooms. Then they will show up as triggers.
It also depends on what kind of device it is. Not all devices can act as triggers. What are you trying to use as a trigger.