No, you only need one account on one server and you'll be able to see posts and comments everywhere else.
Yes, although a few specific servers are blocked by other specific servers, and very small servers may not show many communities elsewhere until their users actually subscribe. But yes, beehaw.org and others work just fine.
You can see a list of all communities here. Also Lemmy federates with Mastodon, not just Lemmy instances among themselves, in case you're also using that.
Thank you so much and also it will take me a while to get used to this (@-@ ٥). I am not familiar with mastodon but how do you use it along with lemmy?