Agree, I think this is one of the best things developers can do. And I think you don't have to be super proficient, you just need to know the subject you are teaching well and be able to explain it.
However, I wouldn't say that newsletter, blog and twitter with thousands of followers is not needed. Although, it is optional, I believe they can give a good boost to your course, in terms of marketing.
And yes, in your post you said it is easy to create a course. I partially agree, in terms of technology and equipment, you don't really need to much investment, however, in terms of effort, I would say it is a huge effort. I started recording one course a year ago, but did not finish :) Now I started outlining another course and strongly decided to finish whatever it takes me to finish it :)
I agree, its a huge effort for the first course but once you do it, you will create a lot more.
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