1) It's a split up snake, describes it I guess haha.
2) The chopped body conveys the states not being collective on things, that they were too much separated from one another.
3) The initials stand for the different states.
4) N.E. stands for New England.
5) S.C. stands for South Carolina.
6) Yes, there is a geographic progression. It starts in the Carolinas (and whatnot) and goes past Pennsylvania, New York, and ends in New England.
7) I would have to guess P (for Pennsylvania), because that's where he lived most of his life, although he was born in Massachusetts which'd be the M. I'm pretty sure it'd be P, though.
8) His fear is that the colonies would lose the 7 years War (also called the French and Indian War), if they didn't join and fight together.
9) The phrase "this Undertaking" is referring to the war going on (7 years War / French and Indian War)
10) The cartoon could have helped lead to the American Revolution by uniting the states, which'd help them in revolting against Britain and gaining independence, as working together works better than fighting separately and alone.