Paul, please note that Instagram is different from other social media platforms (Facebook, Twitter), when it accept only photos and/or videos in a post (perhaps with relevant and meaningful captions). We're not talking about automatic posting to Instagram from other Debian Publicity channels.
In order for Debian on Instagram account can engaging other users, we should create contents just like what influencers done. In Instagram context, this mean that create high quality photos and/or videos for a post. Some posts might not be related to what is already on other publicity services (e.g. throwbacks, inspirational quotes, or random ideas) but the general idea is to engage all other Instagram users so that they will convince themselves to use Debian if they have access to their computer.
Also, when concerning about Stories feature, it also have several engagement feature, like yes/no polls which in some cases can affect development of Debian. Since I have not explored all what Stories features are and how influencers implement them, that the only advice about Stories for now.
Last but not least, Instagram allows up to 30 hashtags. Hashtags is essential in Instagram. However, too many hashtags in a post can look spammy (because the hashtags used is often not related to the post). So I suggest only 5 hashtags or less can be utilized on Debian on Instagram's post.
Regarding Debian presence on social media, I think it will be nicer to have official account maintained by Debian on Social Media SIG, rather than unofficial account run by fans of Debian. Better, Debian official accounts should be verified (have a blue tick).