I'm sorry, but I can only answer one of questions. You should post the others as separate questions in the Q&A section. I’ll deal with diction in this answer.
In the poem “Because I Could not Stop for Death,” Emily Dickinson’s diction (word choice) serves to describe her journey with death and then her grave.
What is striking about the poet’s journey to her grave is how calm and peaceful it is. She does not relate a frightening or calamitous event that leads to her death and burial. Instead, as poem opens, she is already dead, and Death “kindly” waits for her. How often do we hear of death described as “kindly”?
On the way to her burial site, she describes Death as possessing “civility.” When they reach the cemetery, Death does not attempt to seize her and throw her in the grave; instead, the speaker says that Death “pauses” there. Death appears to be pleasant companion.
Finally, the grave itself is not something to be feared. It is simply a “swelling of the ground.” And her time in the grave has not been terrible. She says that each century
Feels shorter than the day
I first surmised the horses' heads
Were toward eternity.