As Bordy had stated, shin bang is primarily caused by the boot. Make sure that the boot cuff area around the shin and calves is evenly buckled and that there is no empty space between the liner and your shins. Go see an experienced boot fitter and have them assess the problem with the fit.
Stance widths will vary greatly as many variables can affect the selected width other than just inseam length alone. Your choice of heel/toe lift, boot flex, and binding angles will all play part in the stance width.