Hi,
Some answers to your questions:
1. Does dokuwiki support the use of different stylesheets within the a single space?
It is possible if you recode the ~/lib/exe/css.php. This php program actually generates the CSS for the current page. So you can generate one specifically for a given namespace.
Not sure if there is a plugin to do that directly.
2. Is it possible to get an xml-representation of a dokuwiki page?
Yes, refer to
http://wiki.splitbrain.org/wiki:export?s=export%20raw