In your profile page/ tab you will see “following”, that’s where you can see you you’re following and also your followers in that tab. Separately at the top (mobile app), you’ll see a star and a “bookmark” icon, that’s where you’ll see your favorites and bookmarked toots.
And as for fun accounts, check out the tweet below that has a bunch that can get you started and fill your timeline slowly. Also keep in mind, you can follow hashtags.
https://toot.cat/@Hashtags/110742042033681800
As for searching, the new mastodon 4.2 I think brings in autocomplete for searches, so you’ll see that implemented soon on mastodon servers.
Hope that helps initially!
Can’t answer your question as I’m also trying to understand but recently Graphene OS has been in the news.
Basically there are apps that won’t work if they have not been authenticated by one of Google’s APIs. Which means there are apps that won’t work if it did not come from the play store.