The Datadog ticket has a list of metrics we'd like to gather there. That's more about timing data and trying to detect borked states (like if everybody's overgrading, or if all submissions stop, etc.). There are no real guidelines for analytics, but the basic rule is to create an event every time there's a user action -- for now we're just confining that to things that are easily detected on the server, like creating submissions, assessments, getting something to assess, leaving feedback, gettings cored.