Papa, firstly
thanks for stepping up to lead this ride.
If there's anything I can help with, just ask. You'll do great!
You can add a message thread as an calendar event by clicking on the
Link To Calendar button at the bottom of the page. As you found, you can add another topic as an event also, but the Link button is designed for this.
If I'm not mistaken the Link button shows up for threads you've started.