At least change your title a bit to distinguish this from this.
I’m glad you’ll go the open-source route. I recommend hosting at sourceforge.
Above all, make the interface clear and easy-to-use. I can help you with that.
What programming language will you use and what platform are you aiming for?
Personally, I like a bare bones sort of thing - I just want to write text which can have links in it. So I might write:
[[DC white-haired man]] would link to a page about my dream character which I call “the white-haired man”. I would be able to write about the white-haired man, find other dreams including the white-haired man, and so on.
Be light on the formatting - allow emphasis, strong emphasis and pictures. Anything more will clutter up the interface.
Would you like more?