There’s no official guidelines. As of now you’ll have to do the research yourself about how mediawiki works or, more easily, check existing pages to see how things are done. Worst case scenario, you screw up somehow. No problem. Rollback or edit by another user and we can act as if nothing happened. Not to mention that you’ll learn something new in the process (ie how not to screw up).
About versions, ideally you’d be updating the wiki with at least the content found in the latest stable build. That said, some people have created content based on older versions (mainly guides, yes, KA101). Outdated information is usually fixed and updated by both regular and occasional wiki contributors. In any case you can always put a warning at the top of the page or section declaring that your info is based on an outdated version of the game.
There’s two easy ways anybody can contribute with: grammar corrections and updating outdated pieces of info. If you, or anyone, spot one of those and has the time and will, changing it is as easy as to click the “Edit” tab at the top of the page and change the contents of the textbox. Then submit the changes.
About spoilers, there’s no official stance. From my perspective, anything that a new player shouldn’t know via the information provided in-game, or just by simple common sense, should be tagged as spoiler. If it’s a whole page, then the pink blurb about spoilers at the top is enough. If it’s just a small bit of text then you might want to use the spoiler tag, which blacks out the problematic content.
2) At [url=http://www.wiki.cataclysmdda.com/index.php?title=CBM:_Power_Sources]CBM: Power Sources[/url] I wasn't sure what the small identifiers right of the titles mean or where they come from (e.g.[b] bio_batteries[/b] at Battery System) so I just left it out. Anybody knows what they are for?
Those are “tags” used in the game code. If it’s there then put it while you update that given section. Most, if not all, of the wiki sections are built by using templates that should automatically translate that gibberish into human once you publish it (or preview it).