Some tips on posting to lemmy from mastodon for your consideration:

• Use a line break in your toot. I believe multi-line toots use first line for the title and the rest for the body.
• Move the at-mention to the end of the last line. The lemmy community still gets mentioned but it gets the mention out of the post title, which looks exceedingly weird in lemmy clients unless you understand how the mastodon integration works.
• Make your own call on hashtags, but yeah... they serve no purpose on lemmy and they make a post looks a bit like a sales pitch. If you're speaking primarily to Lemmy users I'd omit them. If you're getting similar engagement from Mastodon users watching those hashtags as you are from lemmy users on the post then they may serve a purpose. Again, I advise to get them out of the title and limit them to the body though. The look a lot less ridiculous there.
• Use !test@lemmy.ml if you want to play around with formatting and see what it looks like. High-volume test posts with no useful content are welcome there.