Great! That’s an unsupported use case so we’d be very appreciative if you could document your findings in our wiki.
Not sure what you’re referring to. The images contain entire operating systems - there’s no app to shutdown. whonixcheck is a diagnostic tool that checks the type of virtualizer for troubleshooting purposes. It has no affect on the operation of the VM.
You got it. Can’t get any more free than this: Whonix · GitHub
That’s not exactly true and you’ve got our biases all wrong. We actually prefer KVM & Xen (Qubes) to Virtualbox because of Oracle’s handling of past security vulnerabilities. And Virtualbox over closed-source hypervisors since we have no idea how the latter handle security vulnerabilities at all. But Whonix users are welcome to use any hypervisor they like. We don’t have the manpower (or the money) to support every host OS and hypervisor. (Perhaps Microsoft or VMW would like to add Whonix support to their products? You pay them right?) Whonix-13 & Debian Jessie are in need of an upgrade and that is the current priority.
Security Guide - Whonix
Why use Qubes over other Virtualizers?
Whonix for KVM
https://www.whonix.org/wiki/VirtualBox/Security_and_Support_Status