Dear Experts!

One of my clients need a wikipedia like site in wordpress. He wants his visitors to register and after registration the users would be able to edit the existing articles on website. Also he wants customized roles for authors. I need to know which theme would be perfect for this site, is there any theme which already has these features, I am in favor of wikieasy from woothemes. Also please tell me what pluggins I need to install in it for the said features.