A few questions hey?
1) Hey thats my site! TikiRewriteRules, there are also documented on the doc site. Its basically done through some code tweaks in tikilib for the url generation and the Rewrite rule itself is available as apache.
2) Nope 1 user can be everywhere, just depends on your groups and group permissions
3) Accomplished in the Admin->Modules. That module is a custom menu setup through Admin->Menus with links to the forums.
4) Use the banners feature, search for bannerdoc
5) Through Admin->General
6) Looks like it was
The documentation is right here all over the place at tikiwiki.org. Careful searching etc will reveal the info you need. You are welcome to give us a hand at moving the content from here to the doc.tw.o site.