Are there guidelines I should follow on the other metrics shown on the CQ Dashboard, such as '# of feedback messages' or '% first time right'?
Not currently, no. However, you can use # of feedback messages to guide you towards problematic exercises that may need work. Feedback from students often indicates content fixes that you're responsible for, but could also indicate SCT fixes or broken exercises you should tag the Content Quality team in on.
You can use '% first time right' to find exercises that may be too challenging (you'll know if an exercise has both a low '% first time right' and a high '% asked solution.')
For more information on maintaining your course, see https://instructor-support.datacamp.com/courses/course-launch/content-dashboard-course-maintenance.