Instead of installing directly on the Domain Controller (why do something they recommend against if you can avoid it?) consider creating a virtual machine on your server. It will look to the network like a second server, but will be housed in the same box? Much less expensive than adding a second box.

Thank you for the suggestion Walt. I am considering this and run into a couple of questions...

What would I install on the VM? The Domain Controller or Sage and SQL? Currently 19.8 is installed on the main server and it seems like it should stay there because the main server will have more processing power than the VM. If I move the Domain Controller to a VM, will I need to purchase an additional MS Server 2012 R2 license?

My clients' IT consultants did the setups of the VMs. I am not sure whether they needed a second MS Server 2012 license or not. In each case, they put Sage 100 Contractor on the new VM. Its really quite easy to set up version 19 (including license administration) in the new VM and then just transfer the data folders over from the old server to the new VM. Biggest pain is remapping the mapped drives for each user (may be done with changes to the login scripts if used) and pointing to the new VM for the license server. You do want version 19 on the same VM as you will use for version 20.

We did. We had to make sure the workstations were set up as a domain rather than in a workgroup. Other than that it has worked .