1.- The problem is that you want the student's response to be "sometimes private" and "sometimes visible by the peers". You can't have the best of both worlds!
2.- Another Moodle tool that you could use is the Glossary. If you set it so that students can enter their own "definitions", but submitted to approval, and comments allowed, then you could sort of achieve what you want. But it would be complicated for the students.
3.- By "attach" I mean just what I described, i.e. at the end of quiz01 you put a link to "quiz01forum". You set quiz01 Activity completion condition to "Student must receive a grade to complete this activity". You set "quiz01forum" Access restriction to "Activity completion Quiz01 Must be marked complete".
You can achieve this "attachment" behaviour in most Moodle activities in recent versions.
Joseph