At the time of writing, Lemmyworld has the second highest number of active users (compared to all lemmy instances)
Also at the time of writing, Lemmyworld has >99% uptime.
By comparison, other lemmy instances with as many users as Lemmyworld keep going down.
What optimizations has Lemmyworld made to their hosting configuration that has made it more resilient than other instances’ hosting configurations?
See also Does Lemmy cache the frontpage by default (read-only)? on !lemmy_support@lemmy.ml
Unless I’m very mistaken you can not use the same account.
You can, you just must log in to the server/website in which you made the account, then browse over to the server you wish to contribute to or use.
It’s a bit weird, I know. If you’ve got any questions I’ll try my best to answer them :D