Simple way with vhdx files - install ist windows system -- to get started boot a windows install system disk and choose repair system when booting.
Then in command mode create the efi system partition and a virtual disk file (vhdx) large enough for the Windows system you want -. Attach the vdisk, format it as ntfs - don't create this disk as gpt with another efi partition on it. Then install the OS via dism /Apply-Image, install the bootloader to the efi partition via bcdboot and then boot into the Windows OOB as per normal install. Now you've got a nice Windows to GO.
don't forget though to set the PortableOperatingSystem to '0' as well -otherwise update via WU won't work !!!. Also important if you "clone" this system to an internal disk -- if you don't do it then Windows will still think you are running on an external drive !.
plenty of more detailed instructions on this Forum !!.
Advantage of this method is you can have loads of different Windows versions, apps, languages etc -- and they are all activated if your original Windows is activated - (running on same hardware of course).
Just create the OS -- user data etc use other partitions just install the OS plus apps like Office, a browser etc.
Cheers
jimbo