Thanks for posting.
My first guidance would be – talk to your customers about what they would want to see online (will it be self-directed, self-direct plus small group sessions, large group sessions, etc?) and/or how they would want to see what you do face to face be different in an online world? It doesn’t always work to transfer directly from an in person offering to online.
From there I think you can determine the platforms you would need to offer an online course. There are plenty of examples out there Obviously the most cost effective way is if you can figure out a way to deliver content that does not require a facilitator or reduces the number of hours you need one for during a course.
One thing that an online platform may do for you is allow you to use your facilitators, if you have them, to do on demand courses or coaching of teachers, etc. . That could be an interesting change if you don’t do it already.
Unfortunately I know of sites that deliver content as you suggest in your question but not ones that allow anyone to participate and sell their own content on it.