I have a pretty firm grasp on this technique, so I'll answer some questions
Yes. You can actually do the technique with no input, by simply letting go of the joystick. Your character will slide while standing. You can do anything during that, including down smashes without the c-stick.
This is not how it works. If you let go at a certain time before you start running, you will just slide while standing. You can do Foward smashes with this, but you need to let go of the joystick before you press the C-stick for some reason.
Basically, to practice this I would first work on doing it by just turning around with no ledge. All the ledge does is give characters a boost for some reason. Just do the turn around, and let go of the joystick just after you start moving forward again. Timing varies for different characters.
What slides is the same as whatever slides with perfect pivots.