The first thing to understand is that BlueSky servers aren't entirely analogous to fediverse servers. The protocol docs call them Personal Data Servers (PDS), and they handle only a portion of what fediverse servers would handle. Mostly they deliver personal interactions between accounts—"small-world" networking, in the jargon. The rest of your account—your network identity, really—is stored elsewhere. That has implications you should really pay attention to if you're thinking of joining.
Part of your Bluesky identity is recorded as a DID, a kind of secure universal identifier, and to be accessible at all times, your DID has to be registered and stored on a registry. That's similar to how websites have to register their domain names with one of a handful of for-profit registries, and in fact, Bluesky handles are all domain names. So big question #1 is: Who gets to act as a DID registry? Because they will, in effect, hold the keys to your whole identity on the network.