What information do you collect?

None myself.
However, Google records and sends your voice/text messages to the service which I am able to see.
If you use this service then it's compliant with Google's Policy.

How long do you store information?

I don't store anything myself. There are some usage metrics and voice messages which you sent that are kept for analysis to better the service, but that's provided by Google and I don't have control over that.
Perhaps you should ask Google that question.

What happens if I want to stop using your app?

I guess the worst thing that can happen is that you stop enjoying it? Who are you again?

Where do you store my data?

Well I don't store anything. If something is being stored, that would be the cloud!
No seriously, I don't collect your data, but you ARE passing through Google's services... So they probably know.