The high portion of this bar area is 42" which is pretty standard for this type of application (stools are widely available and it also allows room in the backsplash for tile, electrical, etc.). Other common heights are 30" (kitchen table height) and 36" (kitchen counter height). You can certainly do whatever height you want for that matter - you may just need to have stools custom made or altered! I'm 5'3 1/2" and it is easy for me to get on and off a stool at that height. Most common product behind the sink would be a tile of some sort. Unlike showers and tub areas, you don't need to worry about water. There is not enough moisture that gets behind the sink that would require a cememt board behind shower tile. Hope this helps!

Thank so much ! Altho´I don´t really understand your comment of " little water behind sink". I´m in Rio de Jnaeiro where we don´t use dish-washers , so all the washing up is done in the sink and there´´s plenty of splash when Marías washing dishes! My measurements have never impeded me from getting on bar stools with ease! Perhaps in Brazil they´re already shorter?!