Thank you for your message. You might want to have a look at github.com/CMahaff/lasim to sync subs between accounts.
I thought communities synced over instances so if an instance goes down, communities are still accessable.
They are, but not in the way you think: if you follow [email protected] from lemm.ee, and then lemmy.world goes down, you can still see the content of that community on lemm.ee, it does not become unavailable to you.