How to create a page with links to other pages that include image and excerpt?

You have some alernatives.

First alternative is create a taxonomy for pages using register_taxonomy.

Then, assuming this taxonomy is called ‘pages-group’ create a template file called taxonomy-pages-group.php and use the loop to display your page as you want.

A second alternative is create a shorcode that you have to put into pages or post content.

Shortcode should look like:

[pages ids="12,23,34,45"]

You should register the shorcode with add_shortcode (codex) function, something like

function add_pages_shortcode() {
  add_shortcode( 'pages' , 'show_pages_shortcode' );
}
add_action('wp_loaded','add_pages_shortcode');

And the create your show_pages_shortcode function that display the selected pages, something like:

function show_pages_shortcode( $atts = array() ) {
  if ( isset($atts['ids']) && ! empty($atts['ids']) ) {
    $pages = get_pages( array('include' => $atts['ids'] ));
    if ( ! empty($pages) ) {
      global $post;
      ob_start();
      foreach ( $pages as $post) {
        setup_postdata($post);
        ?>
        <li>
          <a id="page-<?php the_ID(); ?>" href="https://wordpress.stackexchange.com/questions/112032/<?php the_permalink(); ?>">
            <?php the_title(); ?>
            <?php the_post_thumbnail() ?>
          </a>
          <?php the_excerpt() ?>
        </li>
        <?php
      }
      wp_reset_postdata();
      return '<ul class="pages-list">' . ob_get_clean() . '</ul>';
    }
  }
}

Of course you can change the output as you want.