Enlazar el estilo del tema principal a tu child theme a través de function.php

// Faster than @import
add_action( 'wp_enqueue_scripts', 'my_child_theme_scripts' );
function my_child_theme_scripts() {
    wp_enqueue_style( 'parent-theme-css', get_template_directory_uri() . '/style.css' );
}

Cargar más estilos en tu child-theme de wordpress

Añadir a function.php de child theme

/** Add scripts & styles*/
add_action( 'wp_enqueue_scripts', 'load_fontawesome_style', 999 );
function load_fontawesome_style() {
      wp_register_style( 'font-awesome',  get_stylesheet_directory_uri() . 'font-awesome-4.3.0/css/font-awesome.css' );
      wp_enqueue_style( 'font-awesome' );
}

Mostrar diferente template single.php por slug

Añadir a funcitions:

function get_category_post_template($single_template) {
global $post;

$categories = get_the_category($post->ID) ;

foreach ( $categories as $cat) {
if (file_exists( dirname( __FILE__ ) . "/single-{$cat->slug}.php" ) )
$single_template = dirname( __FILE__ ) . "/single-{$cat->slug}.php" ;
}
return $single_template;
}

add_filter( "single_template", "get_category_post_template" ) ;