Problem One
Background
Science majors can get in this argument. (Then I will answer the question more directly). Researchers at the University of Hawaii estimate that the number of grains of sand on our planet is about 7.5*10^18 grains of said. This number, large as it is can be equated to the number of molecules in 20 drops of water.
The number of stars in the Universe is many millions of times larger than the grains of sand on our planet. So while the writer is holding just one of these grains of sand, the enormity of the situation strikes her, and that leads her to a very "loving" and [in my opinion] humbling thought.
She compares all of this enormity with how little we actually live, how small our lifespan seems to be. It takes real humility to thank and accept thoughts like that.
Answer
So the key point is contained in the last sentence beginning with "Oh how ... and ending with the period on the next line.
Problem Two
An enjambment in poetry is a continuation of a thought beyond a point where an ending should be. The first 2 lines start out by stating that perhaps it would be best if youth and life were in a trance and should not awaken until a beam of eternity should bring the marrow to a conscious state.
Even though that dream would be of a hopeless sorrow, it would be better than what we live through, to the person who lives though this without the dream.
The enjambment is contained in the thought of the second last line beginning with 'Twere better than the cold reality of waking life ...
Problem Three
I'm not going to explain this too deeply. I think it has answers in what accompanied it. I would pick Two and Three as your best 2 answers. The deep friendship shown by the kind visitor is not that common in abolitionist literature. Most of it focuses on the cruelty of the society and the greed of the landowners and the rights of the colored to be free. This is quite different. It speaks of the kindness of one person willing to break the code.
