@simbleau you got some answers wrong above, here are some correct ones:
We have customers doing this, you just need a single API call to create the forum account from your game account system.
In this case it’s easier to set the forum to use your game account system as the Identity Provider. You can implement the DiscourseConnect - Official Single-Sign-On for Discourse (sso) to allow for that.
Easily done via API.
Easily done via API too!
We have support for webhooks for the Notification event, totally doable without any customizations needed.
The “User Event” webhook covers this.
Also just an API call.
Doable, but it can be quite expensive if the user has many posts.