Please correct me if I'm wrong, but from what I understood so far about the fediverse, someone can host an instance with only one community (or create a community in an existing server) not allowing posting, but allowing commenting and use it as a personal blog. Correct?
That way, Beehaw/Lemmy would be an aggregator of communities and personal blogs which conveniently one could see in the same feed (like in RSS).
Is it doable or is there another recommended way to keep your blog connected with the fediverse?
It's been a few months since I've used it, but Writefreely does federate with other ActivityPub services, so you can follow a Writefreely blog or author (if it's a multi-author blog) from, say, Mastodon (and presumably Lemmy). It broadcasts two sorts of ActivityPub post: Notes, which are short, title-less posts that display in their entirety on other services, and Articles, which display the title and a link to the original post.
However Writefreely does not currently receive posts, so you can't follow accounts from other services from your Writefreely account. The reason is that Writefreely is the self-hosted version of write.as, which started development long before they decided to add AP-support, and which was planned as a suite that breaks out the various functions of blogging into separate apps: write.as for publishing, read.as for following, and remark.as for commenting, plus a few others.
Presumably, those will all catch up and you'll be able to use the full suite for interacting via AP, but the last time I checked, it wasn't quite there yet.