I have my first Legal SAC coming up, and am therefore procrastinating like all hell. I don't remember anything of France AOS 1, but I hope this helps with 'how' to answer the questions. I KNEW THERE WAS A REASON WHY I KEPT MY TEXTBOOKS!
1. In answering this, you might like to address the reasons as to why the system of privilege was affecting economic stability (because I think that's what Calonne would have been referring to). A reason might be the inequality of the taxation system, which led to the Third Estate bearing the majority of the tax burden. As evidence, you could list a few of the taxes that the Third Estate had to pay that the First and Second Estates did not have to pay.
2. This is probably not an exhaustive list of his difficulties, but among these, you should mention that Calonne had to borrow money while his reforms for the fiscal system were being put into place, in order to prevent further financial disaster. To do this, he had to convince the banks that his reforms would be promulgated, and to prove this, he had to show that he had the support from some of the most powerful groups in France. Knowing that his reforms would face opposition from those who where advantaged by the system of privilege, he suggested to Louis XVI that he convoke an Assembly of Notables. However, this caused further difficulties, as the Assembly proved to be less than compliant. Oh, and they also wanted to then scrutinise the royal accounts, which made Louis pretty mad. The Parlements also made it difficult and I can't be bothered going into that, but that's another point that you might consider raising. (But Calonne had been fired by that time.)
3. I can't think of anything for the first part for now, but for the second part, you could say that by 1786, France was facing bankruptcy (and then include evidence regarding involvement in wars, eg. American War of Independence 1778, foreign loans, etc.), with a deficit of 112 million livres, which was almost a quarter of the total income. Your textbook should include some more statistical evidence for this, but that's what I've gotten straight out of mine (Fenwick & Anderson).
4. Third Estate was already over-burdened with taxation. A stat you could quote for this is that in 1766, Turgot (totes stole this from my textbook...), the royal Intendant for Limousin estimated that the peasants in his district were paying 50-60% of the gross value of their produce to the Crown. The system of privilege was inciting growing conflict, as the Third Estate bore the majority of the tax burden, but had no say in how the money was spent. And you know, 'no taxation without representation' and all that.