Yes, the different servers are called “instances,” and each are founded by different admins for different reasons. All the communities from all eligible instances get mixed in to your ALL stream / feed, but of course there is also your personal feed made up solely of communities you’re subscribed to.

I only know that Voyager is a tool, but I’ve no experience with it. I access the Fediverse almost exclusively through web browser.

I’m only a community founder and mod, not an admin. I don’t know much from that POV, but you could always make a new thread in “AskLemmy” or something.

…its usability is fairly rudimentary.

I wouldn’t really say rudimentary; but it’s more complicated than Reddit and takes more time to understand and get the most out of. This is the trade-off for users being nothing more than dollar signs over at Reddit.