Personally I am not a fan of the Mastodon software or side of fedi, but I have had good times on the Pleroma/Akkoma side, and it all works together.
You also don't need to know everything right away. You could make every "mistake", sign up on the flagship Mastodon instance, hear about how you should have other instances, make an alt somewhere else, maybe fosstodon because you like free software, then you hear talk of Pleroma and you look into that a bit. It's fairly common to have multiple accounts, which is good because it provides redundancy. If your instance goes down, flagship or not, you ideally still have a way to view and post. They make it easy to import/export your following list as well, so migration isn't too bad.
It's pretty similar to Matrix if you're familiar with that at all. Initially my friends and I all ended up on matrix.org, then there was some downtime and I realized how fragile it was to all be on the one main big instance, so I made several alts. Now when matrix.org goes down (just happened a week or two ago), I can still post in the group chats I'm in, and anyone else on an instance that isn't down can post, and when matrix.org comes back it'll all flood in for those people as well.
I think it can work and be successful because email was quite successful. Not everyone was on the same domain but we still manage to email each other. You could argue that gmail has a monstrously large presence and that it's harder to host your own mail server these days, but it's all still possible.
No one knew Reddit boards and 4chan boards either; you just knew to go to /b/ or /r/funny. The other boards, the other fediverse servers, are just details that enable other subcommunities to survive. The major community will just route to a single server, and most will probably never use a second