Add a windows 2012 domain controller

I manage a Win2003 R2 SP1 active directory environment with 2 DCs, both global catalog (by the way, where can I find a paper that explain all possible DC installation modes?), both Windows Server 2003 R2 SP1.

I would like to migrate to a Win 2012 server (virtualized) Active Directory environment.

I was thinking something like that:

1) Create 2 VM with Win Server 2012.
2) Join new machines to the domain
3) Promote (one or both?) new machine to additional domain controllers (how should I do that, keeping in mind that I want this new 2012 server to be the MASTER, when dismissed the 2003 DCs ?)
4) Dismiss Win 2003 physical DC.

Please keep in mind that one or more Exchange 2007 SP3 RU10 servers work in this environment.

Any help much much appreciated.

Regards.