If you want to grow Retroarch’s user base, then hiding the new topic button and saying “you need to post 5 times or go hunting for old topics and hope your post gets noticed” is unreasonable, because people are lazy and have the expectation of being able to ask questions without such hassles.
It’s your responsibility to make it easy for these users to find answers, or they will abandon Retroarch.
My own suggestion would be that you need an official QA forum for unsolicited “how do I…” questions from guest users, and you need to throw big “ASK YOUR QUESTIONS HERE” notifications on the front page so people know it exists and they feel comfortable in posting there. Even if you just link to /r/retroarch or something, at least that would get eyes on the questions.