By and large, I think public-facing wikis are very difficult to make succeed. I think that generally people find it difficult to edit other people’s content, especially if that means contributing to some kind of ‘official’ documentation.
Wikis can also be very labour intensive in terms of managing and curating them.
It’s usually better, I think, to provide a draft for people to comment on, or where you want original contributions from folk some kind of Uservoice style forum might work.
Generally, issues around IT and security are the least of your worries with a wiki site – getting people to use the thing will be the challenge.
I wrote a blog post a little while ago about increasing adoption of wikis, which may be handy.
Good luck, and it will be interesting to hear how this project progresses.
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