1a. you go online into your friend roster it'll generate a friend code for you. Once thats done if you want to add people both you and the friend you want to add must ENTER each others friend codes into your friends list under "register"
1b. You should be able to play any mode with friends.
1c. well giving out fc's isn't really about it being popular its more like "hey i think i want a good set of friends to game with" so its worth it and a lot of fun.
1d. When it comes to playing split screen online on GoldenEye 007 [wii] No you cannot its only one player on one wii online for GoldenEye
1e. Yes you can still earn xp and rank up with friends UNLESS you do like a private much or something and not a worldwide/regional match etc