The cohort is primarily used to understand retention. How many unique visitors visited the paywall page (meeting return criteria) every month based on the granularity.
Based on the below request from you, don't use Cohort Custom Dimension rather just using one more segmentation with screens equals paywall.
Now you know which month unique visitors are returning to your website based on the return criteria so that you can understand the retention based on months. If any of the months have more retention, you can deep dive to know what has happened.
Now, here are the answers to your question:
1. Yes, starting from the month you have selected.