Front end for Check out and Video delivery

We are a company that sells videos and photos to clients from different countries. Our current workflow includes charging a deposit at the moment of placing the order and charging the remaining balance on PHYSICAL delivery. We currently have a software to handle the information which was created in Visual Basic and handles the data via Local SQL data base (we have the source code). Our goal is as follow: 1- Modify the Visual Basic software to run the data base from an online source. 2- Create a One Page website with very basic information with a link for Customers. 3- Create a Front end for Customers based on the data base where customers can look up their video and photos via a ticket number and date and are presented with a Check out page based on their remaining balance. Once the payment is complete (either through Paypal or Credit card), a temporary download link is shown. 4- Create a Back end page where we can link the files to the ticket number. 5- Have a way in the back end to view pending sales, completed sales, and totals via filters. Notes: The only thing which is unclear to us is which way is best for the actual file delivery (DropBox, WeTransfer or other services alike) so the programer needs to have knowledge of which service is best for our needs and adapt.