I'm obviously floundering with writing up rules/faq pages, so I don't have good answers for 1 and 2 myself yet. But for #3, there's one I've run into which actually drives me nuts... I don't like rules which police the length of posts.
But that's because I don't headgame well, and I don't personally like posts which go on for three paragraphs of information with only one line of dialogue to respond to (or sometimes no dialogue). I'm happy with content that furthers a thread, whether that response is 1 sentence or 10, so I tend to avoid including rules which dictate that all posts have to be a certain minimum length.