Hi,
URL based https for login, checkout, return page can be done using .htaccess file
Can I see your current setup of Drupal to sell digital files?
Or do you want me to setup a digital shop for you?
I can't help with the process of becoming PCI Compliant but can secure checkout pages, or any other pages which list or transmit customer data which should be enough from my side.
You could also force entire website to be HTTPS to be on the safe side. Also having https pages load non https resources like images,css,javascript files gives warning errors on major browsers. So forcing HTTPs on entire site might be better.
I have an average rating of 5.0/5.0 across 150+ completed projects and a high completion rate.
Looking forward for a reply.
Regards,
Prathamesh Gharat.