Ubercart Invoicing for Purchase Orders

Hi Everyone,

I've been going in circles online trying to find a solution to this problem:

I'm in the process of helping to develop a shopping cart site for a client. We are in the process of getting an authorize.net gateway secured and have successfully gotten test credit cards to trigger email confirmations, etc. with Ubercart.

The thing we're getting hung up on is: the customer wants to be able to sell physical as well as online goods (got that figured out). But they also want to be able to sell multiple copies of electronic books with one-time download restrictions so people can't print or share their links. They also want to be able to sell physical books and online books in purchase order format -- meaning that some people will be able to order them, have them shipped, and receive an invoice for them instead of having to pay by card or check right then.

I found the Ubercart purchase order module and installed it, so P.Os are coming up as an option under payment type now, but I'm not sure where to go from here. Is there something I need to do in the workflow settings, or do I need to dig deeper into actual PHP coding? (I am brand new to Drupal so this is all a learning experience for me)

Where do I go from here in terms of actually having it do what I want it to do-- automatically creating an invoice to send to a PO customer and still processing the order correctly?

What my company wants to avoid is having to manually create paper invoices for every order that's created with a P.O.

To add to the confusion, we're also using an external online data warehouse for the ebook links (which we still have to figure out how to set up so they will only offer a one-time non-printable download), and a print on demand distributor for the physical books.

Sorry if this has totally confused everyone. I'm just stuck and hoping someone out there may be able to explain to me how to customize invoices/purchase order settings once they're all installed and ready. Is this something that will require PHP coding? And if so, whereabouts would I need to do that?

Thank you all for your help. I look forward to any responses!