For serial letters, showing and hiding text blocks depends on the possibilities the word field function IF offers.
Date values must be formatted in the loader using an appropriate format string.
Template elements cannot be used, but must be stored statically.
You can either use the mail merge feature or the catalog function, not a combination of both. A mail merge header or footer may include dynamic data, as opposed to the catalog function. List output, however, is only possible with the catalog function.