How can you get first post, last post and post count in a category?

You could use two separate query to get first & last post based on date.

$args = array(
    'cat' => $comic,
    'orderby' => 'post_date',
    'post_type' => 'post',
    'posts_per_page' => '1'
);

$first_post = $last_post = null;

// get first post
$first_post_query = new WP_Query( $args + array( 'order' => 'DESC' ) );
if ( $first_posts = $first_post_query->get_posts() ) {
    $first_post = array_shift( $first_posts );
}

// last post
$last_post_query = new WP_Query( $args + array( 'order' => 'ASC' ) );
if ( $last_posts = $last_post_query->get_posts() ) {
    $last_post = array_shift( $last_posts );
}

// post count: method 1
$post_count = $last_post_query->found_posts;


// post count: method 2
$category = get_category( $comic );
$post_count = $category->count;