Mald, the plagiarism rule refers specifically to plot lines (ie, copying the content of someone else's story). We all base our stories on the Sims 3, which has a limited number of traits, skills, etc, so it is inevitable that some of those things will be repeated in the various stories. You don't need to ask permission to use whatever supermax skills you want. As for the couch potato trait and your concern that it might be similar to the Man Dynasty, it really depends on how you choose to write the story. If you write a story that is noticeably based on or taking ideas from someone else's story, that wouldn't be acceptable. If you write an original story that is clearly your own creation, you're fine. If you're uncertain, there's nothing wrong with sending a pm to the creator of the original story explaining what you want to do and asking if they have a problem with it.
I'm not sure about the rule for the Gallery. I believe it does require a minimum number of posts, simply because we want to be sure that the people signing up are actually members who intend to be part of the forum and aren't just joining the Gallery for other purposes. It shouldn't take too long for you to reach 10 posts or whatever it is - it's easy to reach that number without feeling you're "spamming" the forum.