Author Template: Number of posts with a custom field's specific value

Hi,
I am preparing my author.php. I would like it to display the following values:
– the author,
– the avatar,
– the total number of author’s posts,
– the number of author’s posts with a specific value of a custom field.
Currently my code looks like this and it shows the author’s name, the avatar and the total number of posts. Regarding the total number of the author’s posts, I am not sure if the code is correct but the fact is that it works.

Any idea how to call the last value – the number of posts by the author with one specific value of a custom field? (after the code goes the loop)

<?php
$curauth = (isset($_GET['author_name'])) ? get_user_by('slug', $author_name) : get_userdata(intval($author));
?>

<div id="author-highlight">
<div class="small-author">author: </div>
<div class="curauth"><?php echo get_avatar($curauth->user_email); ?>
<?php echo $curauth->user_firstname; ?> <?php echo $curauth->user_lastname; ?></div>

number of posts: <span class="nbr-author"><?php echo number_format_i18n( get_the_author_posts() ); ?></span>
</div>