Background and Specialist packages are not, as you say, mandatory...but for beginners, they're<em>highly</em>suggested.<br/><br/>Backgrounds and Links are pretty much as described: mention a kid brother as a Background, and all we know is that you have a kid brother.  We might eventually learn his name, or his favorite color, or that he's married...but only if your character mentions it.  He won't come up in the plot otherwise.  Mention your kid brother as a Link, however, and he's now a character in the story.  Maybe that's good.  Maybe that's bad.<br/><br/>The number of blanks is arbitrary.  The actual character sheet has, I think, five lines or so for both, but since you get three skills and three traits I stopped at three Backgrounds and three Links.  You can have a few more.