Seeking Advice on Launching a Free Course to Build an Audience

Hi folks,
I am getting ready to launch a free course (~4 weeks away) to begin building an audience and I'd like to get some feedback on what I could do to improve my odds of success. Right now I have zero social media presence.

The course will be an introduction to stock investing - something I've done professionally for a little over a decade. It will consist of about 25 lessons that are both published as video and written text and will include exercises and links to free resources to support student's analysis. Side note: the course is on a custom platform and I do web development.

My distribution plan

• All course content will be indexable by google & youtube (email sign up required for exercises)
• I've begun contributing to a few investing subreddits and have tactfully floated the idea of a course in these subreddits, I did get a handful (~20) of preregistrations to a landing page from this
• I'm willing to pay to advertise the free course, although I'm not sure what an email subscriber would be worth. I would think anything less than $1/registration would surely be profitable.

I'd be interested to hear what others have done to build an audience from scratch with a free course.