I would not like to create 18 learning plans, I would create the learning plan for each required competency. The goal of any learning plan is to achieve the highest level of competency. However, in Moodle once a competency is achieved, the progress is updated regardless of the rating. IMHO the rating needs to be tied to a numeric value for the overall progress to the learning plan.
You may be stuck with the 18 learning plans and manual "closeout" of each learning plan as the student moves to the next skill level.
One course, can be done or it can be separate courses. Administratively, one course may be easier to manage. However, you may want to consider, how often would the content be revised? Large courses and are active for an extended period of time, often get "stale." If you needed to rework just a section of the course, it will affect all students regardless of their course progress.
You may be stuck with the 18 learning plans and manual "closeout" of each learning plan as the student moves to the next skill level.
One course, can be done or it can be separate courses. Administratively, one course may be easier to manage. However, you may want to consider, how often would the content be revised? Large courses and are active for an extended period of time, often get "stale." If you needed to rework just a section of the course, it will affect all students regardless of their course progress.