Windows – Virtualbox gives Error code: 0x000000C4 with Windows 8.1 or 2012

You will find some of your questions answered in the article :
Convert your Windows Server 2012 to a Workstation!
which contains many more adaptations than you have asked for in your post.

The section Windows 8 UI Internet Explorer especially shows how to make Internet Explorer run as Windows 8 UI application when started from the Start screen. As this involves registry changes I have not replicated it here.

The problem of using an Online Microsoft Account (Windows Live authentication) is still unsolved in that forum.

That said, I would second the comments that advise against using Windows Server 2012 R2 on a laptop. It would be more preferable to run Windows 8 with Server 2012 as a virtual machine, which would give you a better user experience.

Finally found the answer. It all hinges on Hyper-V and the fact that it's enabled by default in Windows 8.1 Pro (as well as in other Pro and server Windows versions). With Hyper-V running, other hypervisors (like VirtualBox, VMWare and Android emulator) are crippled.

You could, potentially, disable Hyper-V from the Windows Add/Remove Features dialog. But what if you use Hyper-V for development or testing (i.e. WP8 development)?

The solution is to boot Windows with Hyper-V turned off. And the easiest way to do it, is to create a new boot configuration, with Hyper-V off, and boot to it whenever you need to use VirtualBox.

There are several step-by-step guides on how to create a new boot configuration - this one has some screen shots.