4" is a good heigth...it doesn't matter so much but it's easier to work with if they're reletively close to same heigth. i've never scraped them...they seem to like clean cuts better. but try it on a couple if you have room to experiment...or save the experiments for later. i don't pull leaves...they fall off on their own in my gardens.
i usually use extra long branches from the bottom of the plant, especially if cloning late in the veg and those can be cut into individual 4" or so cuttings...