1) allow user to attach file to question and answer and manage this feature with acl rule from backend to;
2) create multilevel points sustem in the backend so admin can set number of questions, answers and attachemnts (if you'll add this feature) allowed for each level of points. For example: level 1: minimum points: 100, allowed questions :5 every mounth (or other predefinied period like day), allowed answers: 10 attachment allowed: 1 for each question and answer; level 2 minimum 200 points......
In this way user wants earn more points.
Let me know please what do you think.