If you're thinking about setting up your own single-user Mastodon instance, I urge you not to do it. The user experience is so broken that it's baffling that anyone would find it acceptable.
The first populates the replies of the home timeline posts you see (as well as profiles of people it finds in those replies) and the second pulls down all the content from instances you select for your followed hashtags (choose mastodon.social and you can guarantee you’ll see most all posts with those tags)
With a small amount of effort and the use of https://github.com/nanos/FediFetcher and https://github.com/g3rv4/GetMoarFediverse you can mitigate basically all those issues. It’s still not perfect by any means but it results in a perfectly usable single user instance.
The first populates the replies of the home timeline posts you see (as well as profiles of people it finds in those replies) and the second pulls down all the content from instances you select for your followed hashtags (choose mastodon.social and you can guarantee you’ll see most all posts with those tags)