Basic membership setup questions

We have some basic questions about the process for the Membership Plugin.

We have it setup for a finite “free trial” period followed by a paid subscription:

1. is the credit card info collected at the time of sign up or at the time the subscription changes (ie., 7 days)?

2. we want to offer them the ability to retain the free subscription if they choose not to keep the paid one after 7 days, how do we set that up?

3. where do we find the unique query ID for each subscription level?