Yes I'm sure it would be tough to market an illegal website. Most directories wouldn't list such a website. Some article directories wouldn't want you to link to that site. Plus many other websites would be hesitant of linking. You would have to focus more on things like forum signatures and blog commenting. Even that might be tough though.
If you copy someone else's material and present it as your own it may be difficult to get your site listed.
Not really, it's very easy to find duplicate content today ... I know 2 very effective ways; 1: with google or any other search engine ; 2: With copyscape.