I'm not sure if there's a way to get trending hashtags (or other things) to automatically show up from other parts of the Fediverse or if we individually have to follow such things. We can definitely follow people from elsewhere manually if we already know the @ handle @ host. It would be nice to be able to choose to get some external content in a more automated way, though.
also good to know about reacting to posts on other servers (tl;dr: buttons will bring you and the post back to ours to react, linking to the original):
Be excellent to each other