PSA: You should know that Settings > Migrate Subreddits exists. All you do is login to your old Reddit account, copy a “multireddit” link, paste it in Voyager and you’ll be able to search the fediverse for those topics/communities to subscribe to.
You may find communities that are missing here if you’d like to run/manage your very own community on a topic you enjoy.
Hope this helps. I just found this feature today and subscribed to a bunch of communities.
No, it just takes a multi Reddit link that you paste, and for each subreddit, it will search for alternatives across the Fediverse.
You can select them one-by-one and subscribe to any you fancy.