role and after that in post-installation steps, you can promote it to Domain Controller.
Let’s start Open Server Manager console (if it was not already opened) and click on “Add roles and features” on Dashboard screen controller” and you will see a wizard.
From Windows Server 2012 we don’t have to run adprep first.
Of course, if you wish, you can still do that but it is not mandatory step.
In this case all of them are running at least 2003 DCs as DFL is set up to 2003 mode, which would not be possible when any of 2000 DCs are still available.
Windows 2003 mode do not support DCs based on earlier Microsoft Windows systems like NT4 and Windows 2000 Another way for that is using Active Directory Domains and Trusts console.
In this place, you can also raise your Forest Functional Level if all of your Domain Controllers in entire forest are running on Windows Server 2003.
You need to only check if connection to DC(s) with mentioned operators master roles is available (it is based on similar solution applied in Exchange 2010 where you do not have to use to extend Schema yourself).