1) Yes. You can install them without the car needing to be lifted.
2) With the ZL1 add-ons and similar variants, you leave them on. One type is magnetic and the other type has a set screw to hold it in place. I have the set screw version and never have taken them off or had any fall off.
3) There are 2 lift points on each side. Best way to tell you is to look under the car and you'll see a very obvious gap in the side skirt. There are 2 pictures in this thread that show where you should jack the car up:
https://www.camaro6.com/forums/showthread.php?t=548253