You don't need multiple accounts, one account can access all different instances, including subscribing to remote communities. You just have to click "All" in the communities or post list to see them, instead of "Local".
Except for beehaw.org defederating from lemmy.world and sh.itjust.works, and I think some defederated from lemmygrad.ml.
Also it should be said that edited comments don't seem to pass across the instances. I think they only sync when the comment has been made.