email address non required

WooCommerce has a very broad documentation, one topic in it is about Customizing checkout fields using actions and filters, you can easily set billing_email to not be required. (code untested)

add_filter('woocommerce_checkout_fields', 'WPSE0309_woocommerce_checkout_fields');

function WPSE0309_woocommerce_checkout_fields( $fields ) {
     $fields['billing']['billing_email']['required'] = false;

     return $fields;
}