Hey Melissa, welcome to the community!
I’m interested, but could you flesh out the spec a bit more? For example in Discourse there are four different levels of watching / following for a category, which have different ramifications for in-app notifications, emails and push notifications.
This feature has been discussed for some time here: https://meta.discourse.org/t/ability-to-follow-and-friend-other-users/1584, and has a #pr-welcome tag, which makes working on it an interesting prospect.
Perhaps you could get a few people together to support the development of something that could be merged into core Discourse?
@P16 you mentioned you were thinking of hiring someone to build this. Still interested?