is your dust jacket jacket design submitted at time of pdf upload or is that done later?
when submitting a file for the proof is the dust jacket design submitted later? Will the proof copy include the dust jacket you designed?
First off, I would suggest you look here >>
You are not in effect
a file for anything. First of all you are uploading files to a Project Wizard. A fully prepared file of pages (docx or PDF) to a Project Wizard. Within the same Project Wizard are three Cover Wizards. You will need the Advanced one. For the latter you will need to create a file to the exact specifications to match what that Cover Wizard needs (and that Cover Wizard has complex needs) for the size and shape of book you selected at the very start (same with page sizes.)
You are not really creating a Proof, but the PR PDF file used by the printers to create your book. The Proof is what you buy to ensure the book looks as you expect it to look before you let it out in to the world, if it is not you have to make adjustments to your original file/s and Revise the Project.