Federalist 51

Q's:
1.) What is the significance of "The Federalist" writings and why is there so many?
2.) According to the note, the different branches shouldn't be able to break into different agencies... was this rule broken with the Executives CIA?
3.) Why is there such a fear of departments in the government becoming independent?
4.) What does the saying, "Ambition must be made to counteract Ambition" mean, in relation to the article?
5.) When James Madison wrote, "Government isn't always  the greatest of all reflections of human nature" did he mean to say there are better methods to run order?

Quotes:
1.) "Ambition must be made to counteract Ambition"
Was this used to say that there has to be a certain goal, of more superiority in order to completely disreguard another goal? There has to be a better explaination for this politically, does it involve, for example a specific bill set out to get passed and and another bill set out to explain furthermore why the bill shouldn't be passed? I'm confused.
2.) "Government isn't always  the greatest of all reflections of human nature"
Even though government is one of the best developed methods of controling masses of people living under similar nationality, there are still flaws to the system that clearly aren't humanly correct.  Politicans can't be considered the best of the best morally.
3.) "Private interest of every individual may be a sentinel over the public rights."
I am interpretting this quote to mean that people would rather throw in their "2 cents" in politics and such for certain issues that will benefit them individually, rather than for an issue that is beneficial to the public.  Keep in mind that I interpret the individual benefit not only as directly beneficial to the individual themselves but also a mark up to their favors in morals, or rights.
4.) "It is equally evident, that the members of each department should be as little dependent as possible on those of the others."
I chose this quote because it clearly underlines for my understanding that each other branches or "departments" in government, although they all are set out to chech each other and make sure one another is doing their job okay, their role is to control their department by theirselves.  For example, the legislative branch and congress may be able to control impeachment of the president (chose to or not) but that is a last resort, not their primary duty.
5.) " If angels were to govern men, neither external nor internal controls on government would be necessary."
Lastly, I chose this quote because it shows any interesting view on why else politics and government are so necessary.  Not only is order needed to be controlled, there also needs to be the realization that man is not perfect and can not always be expected to do what is right, angles wouldn't need government because perfection doesn't encounter confliction.