1. General MacArthur had a successful surprise attack launched on the North Korean army at Inchon, which was west of the Korean Peninsula. When he met with Truman face to face at Wake Island, he publicly accused the president of "appeasement" regarding China. Instead of following Truman's orders, MacArthur did things his way. He thought that the Chinese would not join in the war, so he assured Truman that the Chinese army would not take part in the war when the UN forces reach the Yalu River, the border between China and North Korea. MacArthur was so confident in his success that he promised American troops would be home for Christmas.
2. President Truman assigned General MacArthur as leader of the UN troops. Truman's overall objective was to create harmony between North and South Korea as soon as possible. He was concerned of the Chinese army joining in the war in favor of North Korea, but MacArthur assured him that the Chinese would not interfere when they reach the Yalu River; however, he was wrong. Because MacArthur disobeyed the orders, Truman relieved MacArthur of his position.
3 and 4 are based on your own opinions, so I cannot answer that part. Otherwise, hope this helps a little though it is not much.
