No. Your credit card is not required to sign up for the free plan or trial any of the paid plans.
Channels are owned and non-owned social media accounts, profiles, groups, hashtags and blogs. Each one you connect will be counted as one channel.
Scheduled posts are posts that you compose and publish at a later time automatically. You can schedule posts up to the number allowed by your plan within a given billing cycle, typically a month.
When composing a post, you will have the option to save it to the content library. Saved posts can be edited and shared again manually or reposted (recycled) automatically if you have a predefined schedule for the category they are saved in.
Yes. You can cancel or downgrade your paid plan to free at anytime.