1: (folder question) - "Messages" is a "catch-all" folder for all your messages. If you want to just see your specific e-mail boxes, hide the "Messages" icon, and keep your others visible.
2: (sound question) - Are you sure that you're profile is set correctly? How about making sure that "Mute" is not selected under Volume, or that the Out of Holster or In Holster isn't set to "None"?
3: (Backlight question) - There's no way to change it, unless you download the BBLight app. Not sure if that will actually do what you want, but the flexibility is much greater with that installed.
4: (Cracked Screen) - http://www.promobility.net/html/blackberryparts.shtml