You can convert VL to Retail with the Xdelta files, or you can add WMC to Pro Retail with AlphaWaves AIO program, or you can simply use a Genuine Key from M$. M$ says install with USB External HDD saved image ... there are several reported to be WMC images but I have only tested my image ...
That just displays a different EULA. It doesn't actually affect the install, to my knowledge. The VL section might do something, but the channel just displays the appropriate EULA. If this guy is trying to activate a PROWMC key via phone, I think he needs to activate a pro install via kms first, then do the upgrade thing. I don't think you can do an slmgr /ipk on a prowmc upgrade key. At least I couldn't when I tried.
Unfortunately nope...it´s about 6GB, no clue how big the Delta would be. With my sucking Upload speed that would need years, literally. Also it´s customized to my personal needs. Did this the Sysprep-Route, not that difficult in a VM .
As i activate via KMS, i install ProfessionalWMC (handmade ISO), then the KMSServerService in demand mode and 2 Tasks to reactivate at LogOn and every 24 hours.