That sucks, sorry to hear it. As far as I know, account migration requires the old instance to still be running, because there’s some sort of handshake between the instances to move the data. Do you know your instance admin? Can you find out what happened?
Your social experience will be entirely what you make of it, that’s part of the point of Mastodon. No algorithms, very little ‘suggested users’ outside of trying to help people build their initial feed.
To get the timeline that you want, try looking for a few hashtags you’re interested in. Follow and interact with those people.
Finally, each instance has their own moderators and own rules. There is no central or ‘parent’ set of moderation who manage anything. But usually, if someone gets banned from most instances, it’s for stuff like hate speech or harassment.