I think the end of his part 2 courses is a good point to pick a set of courses that will get you to your desired end state. I would also say that completing these courses would establish sufficient mathematical literacy for many purposes.
I would love to see similar guides for other subjects. Personally, I would be interested in guides for chemistry and mechanical engineering.
While it's pretty straightforward to find open courses/content on Linear Algebra and Calculus, there's very little on, say, Compressible Flow/Gas Dynamics or Turbomachinery, for instance.
If anybody knows of any courses on topics related to the above engineering disciplines, I'd love to take a look.
I also agree that at the end of part 2, one would have sufficient "mathematical maturity" to handle most commercial environments.