Do you have content in all 20 courses? Yes.
Do any users need to be enroled
in any of those beside the main meta course? They need to be enrolled on all 20 courses. Which is why I assumed that if all 20 were pointing to the main course (via meta course links), I would only need to enroll them to the main course.
Are are those just sources
of enrolment information? Sorry, I'm not sure I understand this question. Can you please elaborate or rephrase the question?