A#1 : If you painted over the lines, you will have to re-tape right under or above the pencil lines and paint over them again.
If the pencil lines are over the paint, just use a high quality eraser. Both strategies worked.
A#2 : Take a partially wet cloth ( you kno squeeze it but its still damp) than just wipe softly dont put too much pressure on it though.
A#3 : Try Mr. Clean magic eraser. That thing takes all kind of marks off my walls at home. It does not ruin your paint.
A#4 : Use a new eraser (like from the end of a pencil) just like you would use if it's on paper.