BaseQuatro

Ended up with this, hope it helps someone.

Add to functions.php of your theme

add_action('user_register','my_function');

function my_function($user_id){

        $user_info = get_userdata($user_id);
        $username=$user_info->user_login;

        // create a category with username
     	wp_create_category( $username );

        // create page with username and theme?

        $my_page = array(
        'post_title' => $username,
        'post_content' => '[list category='/$username/']',
        'post_status' => 'publish',
		'post_type' => 'page',
        'post_author' => 1,
		'post_parent' => 105,
		'post_status' => 'private',
		 );

		$newPageID = wp_insert_post( $my_page );

		update_post_meta($newPageID, "_wp_page_template", "cliente-portal.php");

}