Putting together the list of words might prove to be difficult, as there infinite categories (British golfers with first names that are 5 letters). Also, you're going to be competing against content farms. For example, an answer to your first query can be found here: http://wiki.answers.com/Q/Fruit_with_5_letters.

My advice? Write a nice API around the Wikitionary API http://en.wiktionary.org/w/api.php