Yes legally. The original transfer, which was a statute, was REPEALED by the act of secession. If you repeal a law its contents no longer matter - even if those contents say "you can't repeal me." Ask Phil Gramm and Warren Rudman if you doubt that.
Yes it was.
No. It wasn't. I have already demonstrated beyond a reasonable doubt that the language in the two messages differed significantly. To deny that is to fib.
The original transfer was a legal document in which the state of South Carolina ceded all ownership of the property to the United States without condition other than those providing for the serving of civil or legal warrants on people in the fort. The U.S. government did nothing to violate these provisions so the South Carolina government had no legal basis for reclaiming the fort. They had no claim to property that they did not own.
No. It wasn't.
Yes it was. You have demonstrated nothing except that both letters gave, as the primary purpose of the expedition, the peaceful landing of supplies only and that force was to be used on if such a landing was opposed.