I was having the same issue until I watched a bunch of tips including this one and kept trying until it finally happened. Personally I wasn't putting enough pressure on the drag and didn't have the correct hand positioning.

I'm so frustrated. I can't do it lightly, I can manage is loudly.

I use a pretty light paper... Nothing superfine. Or if you have slate a abrasive pad used for dishes will do

Depends on to many factors. Try what works for you. Everyone does things differently.

Green brillow pad works amazing