I've been checking out the different platforms and best practices for hashtags. Some interesting info.
Twitter recommends using no more than 2 hashtags per Tweet as best practice, but you may use as many hashtags in a Tweet as you like.
Instagram practices says you can use up to 30 tags on a post.
Facebook number of hashtags have no limit but a
"results from a study by Social Bakers, which examined how Facebook engagement correlates hashtag use.
(Takeaway: too many hashtags lowers engagement)
Posts with 1 or 2 hashtags averaged 593 interactions
Posts with 3 to 5 hashtags averaged 416 interactions
Posts with 6 to 10 hashtags averaged 307 interactions
Posts with more than 10 hashtags averaged 188 interactions"
https://www.socialbakers.com/blog/2126-the-ultimate-guide-to-hashtags
Lots of opinions, studies and scenarios but it seems like there are some common ideas about number of tags used.