1) You need a separate username (it's not really an account -- it's just a way to keep track of who's doing what).
2) Basically, we want it to grow into a useful Linux resource. Some folks have already started writing great HOWTOs on the site, and that section is improving nicely. But just about anything Linux goes -- app tutorials, software lists, command references, and so forth. The main guideline is: nothing offensive or illegal, naturally!
Click 'Edit' above random pages to see how the Wiki syntax works.