Windows 10 IoT Enterprise LTSC (aka Windows 10 Enterprise LTSC 2019) is for OEMs to build devices with. You can get the Windows 10 Enterprise LTSC 2019 ISO either from a Visual Studio account or when you sign a license agreement through a Microsoft distributor. Your company will have to sign a license agreement any way to get a run time key and license stickers before you can ship a product so it probably be to talk to a distributor sooner rather than later.
As far as creating custom images, the MSDN tutorial is not the best. I have a high level guide Windows 10 IoT Enterprise: Image Development Workflow and a book that covers the details.
-Sean Liming