Thanks for the boot-directly-to-desktop link; I'd just found it as your email notification came in. Typical M$ - obvious and user friendly:
Step 1: Right-click on the Windows 8.1 taskbar, then choose Properties.
Step 2: Click on the Navigation tab, then under the Start screen section, check the box next to "Go to the desktop instead of Start when I sign in."
That bypassing of the login is a great, and, again, less than obvious tip; thank you.
One surprise is how small the resulting VM is. Even with LibreOffice and other software added, it weighs in at just under 10 GB.