Soho

function cwc_rss_post_thumbnail($content) {
    global $post;
    if(has_post_thumbnail($post->ID)) {
        $content = '
' . get_the_post_thumbnail($post->ID) .
        '

' . get_the_excerpt();
    }

    return $content;
}
add_filter('the_excerpt_rss', 'cwc_rss_post_thumbnail');
add_filter('the_content_feed', 'cwc_rss_post_thumbnail');

counter-increment: number 1; 
content: counter(number);