1: The scriptures also say to "pour out" the blood when killing an animal because a life was taken. Blood transfusions don't take a life so the whole point is gone. Also, the law allowed selling unbled meat to non-Jews and eating blood if it wasn't possible not too, which also argues against JWs absolute interpretation. The bottom line is, the blood dogma is just one of many, many crazy ideas from Joseph Rutherford back in the day, including vaccines, aluminum cookware etc. but it's the only one they have no choice but to hold on to as so many people have died.
2: You answered your own question; Noah and his family survived, and they were of course descendants of Adam and Eve that were imperfect and died eventually, so sin was passed on as usual.
3: The scriptures say that Noah took in both clean and unclean animals, although this is an anachronism as the law detailing that had yet to be written centuries later.