How do I create a file download URL?
If you used a Media field, I built a module for this purpose: http://drupal.org/project/media_entity_download - it will take file(s) in a media object and give them an instant download uri. It will not show the actual file path to the user.

If you just have a file field, you're basically looking at what private files option does.

In the end, you'd need a solution that ensures a BinaryFileResponse from a controller, you can see an example in my module.