As long as your instance federates with other instances, there isn’t a need to have a separate account.
For example, I am a member of lemmy.dbzer0.com and you are part of sh.itjust.works and we are able to communicate no problem.
You can subscribe, post, comment, private message across the fediverse.
Some instances defederate with others for a litany of reasons, political, mods/admins, etc. sometimes it’s temporary.
Picking an instance, you should try a few to see which ideology matches yours the best.
Edit: the federation (which is how instances get posts) can even be across applications. For example, piefed and lemmy share posts. Even mastodon and other fediverse sites can share! It’s really cool!