First, the moderation. At the moment it seems like Gorath is the only one with power there, and given the nature of Wikis, that's going to have to change. You can always revert changes, but it's easier to have a good team of mods who can stop any vandalism, attacks, or just plain stupidity and stubbornness before they get out of control. Forum moderators are a good start, but also look at people who show a good knowledge of the Wiki editing system and contribute useful information. These people care about the content and will happily defend it to their last breath, for free, and they're your best defense.
Second, the structure. The Wiki is fine for Gothic 3 as is, but when you start adding more games, you'll regret not having naming conventions and structure in place (ie there's probably more than one game that'll justify a Guides or Maps section). It's still very early on, but it's always easier to correct now rather than later.
I'd also recommend having the basic pages already laid out, so that people can just copy-and-paste existing pages and change the content as necessary. This ensures that all information is there and where it should be for each type of page. For example, imagine a generic quest page layout. It would always include important, easy-to-reference categories like starting location and NPC, effect on reputation, gold/item rewards, and type (kill, deliver, talk, escort), as well as having a textual description on how to complete the quest, with cross-references to give you as much detail as possible (if you want it). Each major type of page (quest, town, NPC, item) should have a template of this sort, to make adding content as easy as possible.