Order Confirmation Conditional Text

[abcisme]

I need to add a statement to the order confirmation email if the order meets the following conditions:

1) Customer's first order
2) Payment module is payflow
3) Order total is over $500

I defined the message in a the email_extras.php file, but am stuck on the if statement in the order.php file to specify who should see it.

if (($total_products_price > '499.99') && ($this->info['payment_module_code'] == 'payflow') && (CUSTOMER HAS NO OTHER ORDERS?)){
$email_order .= NEWCUSTOMERSIGN . "\n" ;
$html_msg['NEWCUSTOMERSIGN'] = NEWCUSTOMERSIGN;
}

Any help would be greatly appreciated. Thank you! :)