Should I add hashtags to Lemmy posts

You can if you want, but Lemmy doesn't translate them, like Mastodon does, and you might find them conflicting with the header Markup.

That, and Lemmy users used to a more Reddit-like structure of posting might get rather annoyed by it, since it would clog up the feed with unhelpful information.

Hashtags don't translate well. They're reserved for markdown headers.

Please no I hate hashtags with a passion.

I can only speak for how it shows up on Mastodon, but over there any hashtags we try and add here just show up as plain text and don't show in the actual tag feed, so it does nothing for discoverability.

#HashtagNo

I'm not sure but I believe from Mastodon's point of view, you are already replying to a group that is the community you're posting to. Or tagging that group in a way. So in that way, it is discoverable by looking at the group, at least in theory.

No.

But if you really want to use hashtags, you can check out Kbin. It's kind of similar to Lemmy and has hashtags.

What's the difference with tags? I think search would be much easier using them.