How can I implement time-based plans in an embedded app?

[Lucifer4]

Hello, I'm currently working on an embedded app.
I would like to add time-based plans to my application, and I have already reviewed the subscription documentation, but I don't fully understand their concepts. That's why I have a few questions:

1. The application will have 3 plans: 2 paid and one free. Should I also create subscriptions using the "appSubscriptionCreate" GraphQL mutation for the free plan? Or should I create these plans only for the paid options?

2. I would like users to be able to choose their subscription and optionally cancel its renewal next month. So that after cancellation, it lasts until the end and does not renew after it ends. Is this possible? After using the "appSubscriptionCancel" mutation, the subscription is "CANCELLED" and does not appear in the active subscriptions of the application, but I would like it to continue until its end. If it is not possible to leave the subscription active after cancellation, what are the requirements for ending the subscription? Is it necessary to use the "appSubscriptionCancel" mutation and the "prorate" argument for refunding payments?

3. Is it possible to simulate the end of a subscription? So I can check the correctness of the webhook operation.