What are the possible copyright and other legal issues faced by an individual in the US running a Mastodon server?
The social network Mastodon https://en.wikipedia.org/wiki/Mastodon_(social_network) has become very popular in the past few months as a possible alternative to Twitter, and there are some important differences between the two services: Twitter is a centralized, corporate-based commercial service, running datacenters in different countries, but operated as one service. Mastodon is decentralized and is run on any number of commercial and private servers by individuals and organizations located in different countries, and server administrators can have little or no formal relationship with other administrators. (The Mastodon software is free and open source and there are no copyright issues with using or modifying the software itself.)
Twitter is a for-profit business which has a legal team, a corporate structure to protect employees and assets, and insurance for civil claims. Mastodon administrators may or may not be organized under a corporate structure or have insurance for civil clams.
One possible source of copyright issues is that Individual Mastodon servers share posts and content by being "Federated," meaning being members of relays that share content between independent servers. This means that content by users who have accounts on other Mastodon servers around the world can appear in the timelines of users on any other independent server, and some of that content my be "cached" or stored on those Federated servers.
For the sake of this question, the Mastodon instance owner - who is an individual and who runs a server in the US and has the sole account and is the administrator of the server - will be referred to as AMastodonAdmin. The Mastodon instance run by AMastodonAdmin will be referred to as MyMastodonInstance.
Can AMastodonAdmin legally "ban" or block users (and their content) who have accounts and post on other servers but their content is shown on MyMastodonInstance by Federation? Can AMastodonAdmin ban users for any reason? Does AMastodonAdmin need a TOS that outlines reasons for user bans and blocks?
Is a AMastodonAdmin liable for copyright infringement committed by users who have accounts and post the copyrighted content on other servers which is then Federated to (and in some instances cached on) MyMastodonInstance?
Does AMastodonAdmin running MyMastodonInstance in a US datacenter need to be aware of GDPR https://gdpr.eu/ ? Does AMastodonAdmin need to respond to requests by EU members whose posts were federated to MyMastodonInstance?