Blood Analysis

by G.H. Monroe
(Central NY, USA)

I am a fiction writer and have an idea for a novel. The idea, however, hinges upon the answer to these questions:

1) What percentage of his/her blood can an adult human draw and continue to survive and function without medical assistance?

2) What is the shortest amount of time that the human body will take to replenish that drawn blood?

3) How well can a forensic expert tell how old samples of blood are? Assume that they have been drawn every two weeks and kept refrigerated without preservative.