Awesome suggestions!
Adding a "Random Community" button that just takes you to a random Community in any instance would be nice too. I used this a lot on Sync to discover smaller subreddits.
Also, the option to choose when/how posts are marked as "read". For example, it can be after you open the post, or interact with it in any way (upvote, preview...), or just scroll past it.
Yes!! And also the ability to "Favorite" communities or community groups so that they appear at the top of the list.