How to open modal form on page load
I'm not sure why you would want to automatically load a modal when the page is loaded, IMO that's a bad user experience. But if you must, you can use a bit of jQuery in the theme to make it happen. Maybe something like the following:

  /**
   * Open Modal window on page load.
   */
   Drupal.behaviors.openModalOnPageLoad = {
    attach: function(context, settings) {
      // Just create some kind of ID or class for the modal link, add whatever extra
      // classes you need to be more specific if necessary.
      $(".page-node-number #myModalLink").click();
    }
  };