Quick entry. So I need to do a lab for a client and I need to recreate a lab for them. They asked, how did you do it? They further said its really tiring going to UI route creating differencing disks and VM (That’s why!). So I told them I just to use PowerShell. This is being done on My Windows 8 Desktop with Hyper-V installed.

Command is
New-VHD -ParentPath "<path>.vhdx" -Path "<path>.vhdx"

How about VM?
Note: Just make sure you run as an administrator!
New-VM -Name "<name>" –MemoryStartupBytes <int>GB -SwitchName "<Switch Name>" –Path "<Where you want to save>" –VHDPath “<Path\VHD.vhdx>”

As you can see, you do not have the parameter to configure how many virtual cores to be assigned to this VM. You do this:
Set-VMProcessor “<name>” –Count <int>

This is also true for Dynamic Memory:
Set-VMMemory <VM Name> -DynamicMemoryEnabled $true

PS.
All info of these are available at TechNet (Hyper-V Cmdlets in Windows PowerShell):
http://technet.microsoft.com/en-us/library/hh848559(v=wps.620).aspx