Although I have though about Windows 10 with Microsoft OneDrive. The only big problem I see if you have a laptop is any external connection could be reset should you disconnect the devices and use the laptop at a different location.

The data rate on a usb drive will be slower then a drive connected to the motherboard. Some laptops even have the ability to add an extra drive. If it's a laptop you can get a larger drive and image the old one to the new one then swap them. If it's a desktop you should be able to add a second drive very easily. There have been posts that users have installed to a usb drive but no one have reported how long it works.