Migrate Exchange 2003 cluster to 2010 or 2013 with DAG/CAS Array

I have to migrate from exchange 2003 to 2010 or 2013, this is the setup

Forest n Domain Functional Level: Win 2003

GC/DC : Win 2003

Exchange : Clustered Exchange 2003 Std

Mailbox : 170 Users

My domain is a child domain, the parent and other child domains are also using exchange 2003 only.

i have 2 new servers, my plan is , install win 2012 with HyperV , create 2 VM for each server.

Host1 : VM 1: Exchange 2010 MBX , VM2: Exchange 2010 CAS/HT

Host2: VM 3: Exchange 2010 MBX , VM4: Exchange 2010 CAS/HT

Create DAG for VM1&3, create Client Access Array for VM 2 & 4

Is it possible ? do i need a witness server for DAG?

Appreciate for all help !