To answer a few of your questions;
1. If you do it incorrectly, you may end up Bricking your entire console. This will essentially turn it into a paperweight or a doorstop.
2. You have to downgrade your console using a flasher. If you have a Super Slim PS3 (The sliding disc tray model) then you are out of luck.
3. No, not all would work and you have to be careful where you get them from.