In reviewing the documentation for the Office 365 Click-To-Run deployment toolkit, it appears that the tool allows you to download a customized installation to a network share, and then distribute it to users.
I have many satellite offices, with all of the larger ones having internet connections that allow for unlimited bandwidth. Is it possible to leverage Microsoft's own CDN, rather than host these files locally? I would rather computers affected by the group policy download a customized version directly from Microsoft's CDN. Is this possible?
This can be done.
Take a look at the Office 365 ProPlus Configuration XML Editor: https://officedev.github.io/Office-IT-Pro-Deployment-Scripts/XmlEditor.html
From the "Add Product" page, you have the "SourcePath" option.
The tool here is just to make your life easier, you can create a manual XML file and it will still work.