Hey, that's a great prospect for one of the answers to these questions. I didn't even think of that one.
I believe that when the Lord does something, often there is more than one reason for doing it. He's a complicated God, so there are probably a number of reasons He required these practices for women.
Some of the reasons women were quarantined during menstruation may have been for basic sanitation to keep disease from spreading, for the rest and health of the women, and to keep the people aware of the sanctity of blood. The shedding of Jesus' blood would become the keys to the Kingdom in the future.
Can you imagine being a women back then? It was tough work. They couldn't go to their local grocery store and buy ready made meals, they didn't have cloths washers and dryers, nor could they go to the store and buy cloths or bedding for their family. They even had to prepared the ink to dye their clothing with. Their list of chores was endless. I would love to be able to go to the local quarantine shelter for a week every month, hang out with my girlfriends, chat, rest, and eat all the chocolate I could get my hands on. I can just imagine the women back then shout, "Yahoo!" whenever they discovered their cycle had come around again.
The second question may give us a clue to just how much our Lord loves us. The differences in times that the women were to be secluded shows that His aim wasn't to say women were bad for some reason, as some people are tempted to think.
I believe the time was shorter for boys not because girls were somehow less than boys, but it was for the benefit of the fathers. The birth of a boy meant that he would have an heir, someone to help him with his work, and the family name would carry on. Therefore, I think the Lord, in his loving grace, allowed the time to be shorter so that the fathers could celebrate the birth of their son. The time may have been longer for a woman after the birth of a girl for the mother's sake. She would have longer to rest and dote on her new little girl with all of the other women in her community.
These are just some thoughts I had concerning these verses. They are by no means an attempt to assume what the Father really had in mind. But, when I think of the Lord as a loving God, I'd like to imagine He may have had something like this in mind.