1) The empty PDF is typically an issue with either
-) incorrect HTML in the payment method name/description/info, or
-) a shipment/payment or vendor logo in an unsupported image format (e.g. gif)
See e.g. the VM forum:
forum.virtuemart.net/index.php?topic=116347
2) What do you mean with "ordering of the invoices"? My plugin can assign order and invoice numbers of your preference (e.g. VM-2014-0001), which can then be properly sorted by filename / order number. The default VM order numbers (random strings with a counter appended) do not allow sorting invoices by invoice or order number.
Is this what you have in mind?
Best rergards,
Reinhold