I have been using Lemmy for 20 days, at first I opened an account at Lemmy.world because you can join without writing a text and waiting approval. I have been enjoying the experience overall but despite the admin teans best efforts Lemmy.world has been experiencing some serious performance issues. If you want to avoid that join a smaller instance, preferably hosted in your country. I joined discuss.tchncs.de today and everything is so much faster it has added benefit of being able to see beehaw.org posts too. It will improve not only your but all other Lemmy.world users experience too.
Currently Lemmy doesn’t support account migrating but it is technically possible afaik. It might get added in future but currently you have to sing up from sracth. Hovewer I would say having a Lemmy.world account in addition is probably a good call.