First of all, thank you for trying this and also for actually posting about it. I've asked 2-3 times in the big thread and nobody ever answered.
Secondly, about VSS, the Boot Camp 5 driver package includes an HFS+ file system driver for read-only access in Windows. This driver is only compatible up to Windows 8.1. If you use it in Windows 10, it prevents VSS from working. I suspect this is what is happening to you. You can either uninstall the HFS+ driver and live without read-only HFS+ access, OR install the HFS+ driver from Boot Camp 6, which does work with Windows 10 and therefore does not break VSS. You can download
that driver from this thread.
Lastly, I think you are on the right track. Windows doesn't "like" to be installed on an external drive, but that limitation can be overcome with various workarounds that can be found on the net. (I have not tried any of them so I have no recommendations.)