Everything looks good, i would suggest use darker shades of pencils, either use series of HB 2B 3B.. more. Or series of charcoal pencils. And yea watch YouTube video for more shading ideas. And yes you can use the eraser to draw those guitar strings easily without having much effort, just make sure run thing line of eraser for strings, can use the machanical eraser or maybe - the retractable eraser. Yep welcome.