To your first question, Yes. I don't know if you heard of them but for some time they had these gadgets like big rubber bands used to constrict bloodblow to a muscle to get it to work in an increased anearobic state. This is only true the longer the exercise or set is. Since initially it is all anearobic. You can get that from the article from the second post.
For your second question, Are you asking if you hold your breath for four straight sets even in between, or strictly talking about performing sets not even thinking about breathing?
Third you want to increase blood flow when performing exercise because it allows you to exercise longer and harder and cause more muscle damage. In the end the point of your exercise is to increase cns ability and/or maximum repairable muscle damage. So more blood flow will allow you to get in more reps to damage more fibers causing more repair.