1. Fields - title, question, answer, link 1, link 2, date created, updated, etc.
2. Moderation and Admin entries only - or other trusted members
3. Some forum threads could be moved there though an interface which would allow editing (removing quoted, threads, extra material, etc.) while it was on the way from forum to QA engine.
4. Separate Search engine for QA
Another option would be a bridge to an existing open source QA engine - here is one with a WP interface and others: