comments_number not displaying

You need to change the code you’re using from

<div class="post-meta">
    <p><?php the_date(); ?> | <?php the_tags('tags:', ', ', '<br />'); ?> | <?php comments_number( $zero, $one, $more ); ?> comments</p>
    <?php comments_template(); ?>
</div><!-- end post-meta -->

to

<div class="post-meta">
    <p><?php the_date(); ?> | <?php the_tags('tags:', ', ', '<br />'); ?> | <?php comments_number( 'no responses', 'one response', '% responses' ); ?> comments</p>
    <?php comments_template(); ?>
</div><!-- end post-meta -->