Show top commenters without using a plugin

I’m trying to create a small list of top commenters in my sidebar.
I don’t want to use a plugin, so I was googling for codes.
All I could find was the following:

function top_comment_authors($amount = 5){

    global $wpdb;

    $results = $wpdb->get_results('
        SELECT
            COUNT(comment_author_email) AS comments_count, comment_author_email, comment_author, comment_author_url
        FROM
            '.$wpdb->comments.'
        WHERE
            comment_author_email != "" AND comment_type = "" AND comment_approved = 1
        GROUP BY
            comment_author_email
        ORDER BY
            comments_count DESC, comment_author ASC
        LIMIT '.$amount

    );

    $output = "<ul>";
    foreach($results as $result){
        $output .= "<li>".$result->comment_author."</li>";
    }
    $output .= "</ul>";

    echo $output;

}

I already modified it because I also want the post count and author url to show up. I also want to add a gravatar later on.
However, it just displays everything next to each other:

$output .= "<li>".$result->comment_author. $result->comments_count. $result->comment_author_url."</li>";
    }
    $output .= "</ul>";

    echo $output;

}

Whenever I try to add something, I end up getting an error message. I’m pretty sure I need to modify the little code above if I want to change the way it’s displayed, but HOW?! :/

This is how I call the function, so no room for customization other than in the function.php, right?:

<?php top_comment_authors(); ?>

I’m not really good with PHP, so I wonder how I’d do something like this:

[gravatar] “commenters-name-as-url-if-available” (comment-count)
e.g. “japanworm (45)”

If anybody could help me a little, that would be great.
Thanks a lot!