Server 2012 and Hyper-V implementation

Howdy folks, please forgive a Hyper-V newbie for what may be a simple question!

I wish to set up the following scenario, and I am hoping that someone can sanity-check this to make sure I'm not missing something.

I want to get a single physical server with 3Tb drive space using 10k SAS drives in a RAID-5 array, and around 64Gb memory and a pair of Xeon processors - something like an HP Dl380 G9.

On that I want to install Windows Server 2012 Standard as part of a workgroup.  I then want to install the Hyper-V role, and set up the following virtual machines:

(1) Active Directory controller with space for file and print sharing.
(2) Exchange Server 2013 (domain joined to the AD above)
(3) SQL Server (again, domain joined to the AD above).

I do realise I will need 2 licenses for Windows Server 2012 Standard as the number of VM's I want to create will require this.

I am looking to have this used by about 15-20 workstations - the SQL server use will be fairly light (it's going to run one database that's used only be a few users).

Questions:

Is the overall system architecture (Server 2012 workgroup as base, AD, Exchange, SQL as VM's on top of that) correct?  Given real world experience on the part of readers, is the proposed hardware sufficient for this task - if not, what is lacking and needs improvement please?