That was an eye opener for someone who was thinking of setting up an instance. Obviously there are risks to federating posts from other instances, but I wasn't ready for this.
E.g. start with the biggest ones and maybe some that are specific to your interests. Over time you will see people resharing posts and commenting on threads from other instances and you can add those as well.
If you run a server for other users you could have an account set up for your users to ping with servers they want you to add.