Hello, as Jane is offline right now I thought I would answer your questions.
I (and I believe Jane does too) prefer to use thinning scissors on the ears as it is a sensitive area. It may be ok to pluck the hair on dogs that don't have a heavy coat, but generally scissors work best.
If you feel on the outer edge of the ear, you will feel a little knobbly bit. I use this as a guide when tidying the ears as it is about 1/3 of the way down and that is roughly how far you should go.
hth