How to stop autosuggest in node author field and write our own?
You could write a small module that implements hook_form_alter in which you remove the autocomplete functionality for this field.  This should convert it to a textfield.  However, this will certainly break if an author name that is not also the username of a user is inserted, since this field is used to populate $node->uid, which must have a valid username.

A more viable solution would be to create a vocabulary of your author names, and a taxonomy term field on your content type (pointing at that vocabulary).  And then display this field as you desire.