I believe, after some time, such works become public domain and may be freely copied, published and distributed by anyone. How long is that period of time? 60 years after the author's death, or after publication? Is this law international or are their variations from country to country?

Copying is, I believe, permitted, as long as the purpose is academic, and the copying will not effect sales of the original in any way. How exactly is this defined?

Who holds the copyright of Tolkien's work. What or who are the Tolkien Estate and Tolkien Trust? What is the difference between these organisations? Who holds copyright over yet unpublished documents?