3: I do not think 'because the South was agrarian' is a sufficient answer. Was it ideological, even though true abolition movements were quite rare? Was it economical? How would ending the slave trade be economical (perhaps poor whites did not want to have to compete with free labor?) I don't accept the doctrine that the North marched South to 'end slavery,' by and large, so I am curious why they chose to end it in their own borders. So far, research online has only given me timelines and debates (the state voted to end slavery/there was tension in the states regarding the issue of slavery), but rarely does it get into the whys.
4:I don't think that the Civil War could have been avoided. Both sides were heading for the conflict for many years prior to it's start. The election of Lincoln forced the Southern states to force their hand and resolve to leave the Union. And Lincoln wasn't about to let them leave it without a fight.
5:Need more detail
Hope this helped