Teaching with Moodle

'For now, I've been setting individual courses for students'

---You must be a hard working teacher!

Quiz is One(teacher) to Many (Students). Student can't see each other. So, you never need create courses for individual student.

After you setting up a Quiz or an Assignment, you can simply user News forum to send a notification to all students.

If you don't have too many students, you can create a course for each one where they get your individual attention and admit them to other courses when you address them in groups.

Nothing wrong in one student courses. Afterall by individual attention you mean an extra individual course exclusively for that student. In that course you can use all tools like quiz.

(If I understood moodlese correctly)

In my opinion, you can also use the groups at course level  with separate groups in the Groups settings in course settings and assign individual users to different groups. Afterwards you can use the news forum to send the notifications to all students.

Hope it helps!!

Jaswinder Singh