1] setup a wordpress blog. New Question == New Blog post. Hold all comments for moderation. Allow comments that dont have answer in it. Allow answers later. This is quite tedious.
2] Wiki- I didnt get How it will work. User's answers will still be visible to others. Please explain what you mean, along with live example if possible.
3] Custom Script - Will be like Challenge series. Much like hellboundhackers.org User will register > will get list of challenges. He can post his answer. Admin/Challenge poster will accept answer > user will get some points.Instant acceptance of answer if question is choice based. If User has some query, he can post on forums or can PM someone. This will take some time.
I think that the idea of using a wiki was to be able to get something simple and quick to set up to start with.
Starting with Something like 2 tabs One for the question and one for the answer that is posted a few days after the question,
Then, setting up a third tab where people can post and reply. Some sort of forum.
The main reason to go this way is not because it is the best solution, Of course a custom application desing for this thread could be much better, but also it would require for somebody to invest a lot of time in something that we cannot be sure will work.
I will sure do every thing I can to get it work, and I am sure that some people from the forum will work with me.
If we see that this is working well, it will always be time to change from a wiki to something better. Also, a this time many ideas came, but nobody knows exactly what would be the better way to go.
I think that we should just start it, we will see how it goes and how exactly it should work. Then, it will be time to think about setting up something that will be working the best way possible