If you want people to notice your posts on the Fediverse, use hashtags!
Most Fediverse platforms like Mastodon only allow searching by hashtag, so if you don't include tags your post won't show up in search results.
It is ok to use lots of hashtags if your post deals with lots of different topics. Don't be embarassed to have a list of tags at the end, for example.
@futureisfoss
That one depends on the instance, even though 500 is a hardcoded default. The one I am on, for example, has around 65k. I didn't like the 500 character limit either, hard to have a meaningful discussion going with that low amount.