first off shishio was male,
Let me try to deal with the 4th and naruto. The child was choosen we do not know and the mangaka has said once in jump manga that naruto past will remain a mystery because it gives many people to think. So analysis whether he is or isn't is a waste of time.
now for the cheapness of the kyuubi.
the kyuubi has no flaws comparing it to a bloodline limit is unfair all limits have their weaknesses. You can't name one that doesn't have a flaw of some type. Kyuubi healing ability is crazy now that naruto can heal the holes the sizes of baseballs instantly. Kyuubi is unstoppable if he allowed to take complete control