Lemmy/fediverse questions

Hi,

Lurker refugee from reddit here. Being a network engineer, I'm somewhat tech-savvy. But I'm having a hard time getting to grips with lemmy, or I should say the fediverse. I understand that it's a bunch of servers/instances that connect/federate with each other. I also just learned or understood why I can't login with my user account from lemmy.world on lemm.ee. It's like email providers :)

But I've got a few questions that maybe someone who knows more about lemmy and the fediverse can answer.

• What happens to accounts, communities and posts when its instance decides it's been a fun few months and decides to shut down?
• Can someone register with my username on other instances, or is my username "taken" across the fediverse?
• If so, how are spoofing and/or scams using my username but on a different instance handled?

I'm starting to understand that it's not my data that is federated, but only links to the data in other instances. Would that be a good understanding on how the federation technically works?
All my account data is located on my "home" instance, but in turn my posts are stored on the instance where I posted or commented and linked to all other federated instances.

I could try my 2nd question myself, but I don't like creating more accounts than what I need.

Thanks!