Windows To Go is only in the Enterprise version of Windows. There was a post a few days ago, where someone had ported it to other versions, but its gotten lost in all the mess over release/activation questions. Or you could try WinToUSB that can use any version of Windows.
You've got to remember that you intend to use WTG in a way it was not intended to be used, as such you've got to either go through the proccess as set out by MS or find work arounds. WTG is only meant to be used by Enterprise SKU's and be activated by KMS. So having one system as a centralised base or 'Mother(Ship)' that does all the backend work makes alot of sense for any company. Whether you want to maintain one or two systems or not is irrelevant, in that scenairo. Making your VHD's manually is a way of avoiding this, but it also means, alot more work for you and you don't get a 'proper' WTG setup. Now if you want to use a customised WIM for your install, you have to do that work anyway. And as Pisthai has said the standard WTG setup doesn't work for him. So he goes a different route, which does. It sounds to me that going the DISM route would be best for you, As you said you want it to contain your apps and files so build a custom WIM and apply it to your VHD. And you want to be able to access any other drives on the PC's you connect too, which a standard WTG setup will block, but a normal Windows setup won't. Also, it won't be as H/W independant as you'd like it to be. Everytime you connect it to a new PC, it will have to find or download new drivers for that PC's H/W. This will build up over time, which speeds up the process but also takes up space. I'm not sure what the difference is between KMS and MAK keys but if you use a 'Mother' to create your WTG or WIM. I'd only use your key on the VHD, you can use the Enterprise Eval version for 90 days, thats plenty of time to create your WTG or WIM. I don't know why Pisthai had to install all his apps manually on each WTG Drive. But, my guess is he was using a standard WIM not one he created/captured from a test system. Like I do. As for a W10 'Upgrade' Enterprise SKU's aren't entitled to a 'Free Upgrade' so why go through the hassle of upgrading when a clean install is better and faster. Same goes for your VHD, why do an upgrade on the VHD. Just make a new one, with a custom W10 WIM that has all the apps and files you need. Personally this is what I did. I backed up my Doc's and Folders from the W8.1 VHD's, made new W10 VHD's then restored my Doc's and Folders to those.
I just tried using the recent version of WinToUSB and mounted some VHDs {on my local SSD} I'd created using Powershell and it doesnt show those Drive letters as DESTINATIONs at all? What am I doing wrong? Or do I need an older version of W2Usb? I noticed some similar posts on their forums with no final answers. Is it something they had in older versions?
I couldn't help you with VHD's because we didn't use them at all! As I wrote in my post, we using those WinToUSB (WinToGo) for to service our customers, and for that, WinToUSB is much better than WindowsToGo! One thing you should realize: if you'd crated an WinToUSB Drive, that will work as external only cottectly, but internal as you mention in your post above.
You don't need to manually create and mount a VHD when using WinToUSB to create a Windows To Go drive, WinToUSB will automatically create a VHD on your usb drive then mount it.