Technically, the wiki allows for HTML tables. However, as part of a past effort to give our wiki a set of standards similar to other major wikis, we ask that all tables use wiki syntax, rather than HTML. You'll find that, for the vast majority of the code, the syntax is identical. If you prefer making tables in HTML, or even your entire wiki page, feel free to check out this cool converter -- http://labs.seapine.com/htmltowiki.cgi as it converts HTML to mediawiki syntax.
The wiki is not a place for storing or displaying fiction. We, like Wookieepedia, have based our wiki on the ideas of the original, encyclopedia-focused Wiki. All articles are to be written in an objective, third-person point of view, describing events in a historical or biographical fashion. There should be no dialogue or internal monologue. I liken it to this: In fiction, you write a story about your character. On a wiki page, you make a record of the events that transpired in your fiction.
In the near-future, we'll have more guidelines on what is and isn't appropriate for various wiki articles.
a) As far as I know, the Brotherhood does not currently have a resource for members to upload and display their own fictions (or graphics or whatever). Your best bet is to create an account on a site that allows you to store and share documents (google docs, dropbox, etc) and then generate links from that to put in your article.
b) Although our wiki doesn't currently have a sourcing and references help page (it will soon), feel free to use the Wookieepedia's -- http://starwars.wikia.com/wiki/Wookieepedia:Sourcing This covers how to be use references throughout your wiki page and gives you an idea of when and why you should use references. For a DB example, (and because it's the only one I have on hand), check out https://wiki.darkjedibrotherhood.com/view/Aidan_Kincaid If you edit the page, you'll see how I've set up references and sources for quotes, and then added a heading to list them all at the bottom.
No. Same reasons as above. Fiction is still fiction, regardless of how you add it to the wiki.