There's an industry standard there. If it was me and I was called upon to write a technical requirements document for a new Wiki, I'd start with the features page of Wikipedia. Then, I'd attempt to use the tools in a dev operation, determining the strengths and weaknesses of the implementation. Wikipedia is built for the masses, so there's certainly improvements you can make on the interface and layout that will better suit your needs if you choose to go this route.
Documentation and a roadmap is key to less factoring in development (regardless of language) If you go in without a plan, you'll inevitably cause yourself headaches and require yourself to go back to refactor. It's always better to build with a goal in mind and stick to a quality plan. Obviously, we all know in this industry that the other key is to realize that often those plans are well intentioned but woefully short, so those of us who are most able and willing to adapt are going to be the most likely to succeed.