Hi Andrew,
Thanks for posting. Like we covered in our email it is possible to achieve this but it’s not the sort of customization we can guide you through.
Tickets are stored as posts and the ticket numbers reflect the corresponding post ID, so you would either need to work with the WordPress API/directly with the database to modify this or else create your own parallel numbering system.
Generally speaking it can’t just echo the order number because it’s possible to have multiple tickets per order.
Sorry we can’t offer up more on this occasion, but we can definitely leave this open and see if anyone else has ideas/tips.