So let’s flesh out a bit why we need one domain controller, one member server for Exchange and one member server for SharePoint.
First let’s lay the foundations of what CANNOT/SHOULD NOT/and is really and truly not recommended to be installed on a domain controller.
First up is SharePoint 2013:
Certain Microsoft SharePoint Server 2013 installation scenarios are not supported:
“You install SharePoint Server 2013 on a domain controller. This scenario is supported only for development configurations and not for production configurations.”
Next up is Exchange…which other than on SBS isn’t supported on a Domain controller:
Exchange resident on domain controller that is not a global catalog server:
And specifically : http://technet.microsoft.com/en-us/library/aa996719.aspx
Installing Exchange 2013 on directory servers