Course: you can “archive” a course by closing it (modifying the “end date” in Studio-> Settings -> Schedule & Details ). Learners who were enrolled in the course will still be able to access it from their dashboard, though.
Section: You can delete sections in a course, but not “archive” them per se. As a backup/archive, you can download any course and keep the file somewhere for future use or reference.
You can’t delete courses from Open edX (at least not without technical knowledge). What most users do is just hide the course from the catalog (Studio -> Settings -> Advanced Settings -> Course Visibility In Catalog).
Yes, if you read the documentation I provided and search for the word “coupon” you will find this section about coupons. I hope this helps!