Teaching Selenium with interactive online-course

In this talk, I want to tell you how we created one of the most welcomed massive courses on Stepik - "Automation testing with Selenium and Python". How to teach automation testing essentials, when the number of learners is huge and completely unpredictable? How to minimize manual homework grading to have more time and energy for non-trivial questions and discussions? What our benefits were from this online teaching experience, and why we started all this.