For the first part :

If the arrow hits from behind and does not penetrate the shoulder blade, it would be fairly little blood loss. If an arrow would penetrate the damage could be severe. The Major blood vessels in the shoulder region are the Arteria and Vena axillaris. They maintain blood flow for the complete arm, and are fairly big vessels with high flow. If the arrow doesn't tamponade the wound properly it is very well possible to die from bloodloss, especially if the vein is injured (Arterial bleeding is usually better manageable, even though I am not entirely convinced that this is true for mediveal surgeons as well).

So basically an arrow to the shoulder could be anything from 'meh' to life threatening. Big problems were always wound infection and if a joint was involved stiffening of the joint.