Perhaps you’ve already figured it out, but maybe this will help others. I think these will apply site-wide, but you could write the functions with some conditional statements to target a specific form.
Visual Editor as Default
// Set Visual editor WYSIWYG as default
// https://wp-snippets.com/set-default-editor/
add_filter( 'wp_default_editor', create_function('', 'return "tinymce";') );
Show “Kitchen Sink” Options by Default
// Show "kitchen sink" editor by default
// https://wpmu.org/show-the-wordpress-kitchen-sink-options-on-the-editor-by-default/
add_filter('tiny_mce_before_init', 'my_unhide_kitchen_sink');
function my_unhide_kitchen_sink($args) {
$args['wordpress_adv_hidden'] = false;
return $args;
}