System Center 2012 Configuration Manager ist now available nearly since more than 1 and a half-year, and the biggest question to start a new Project is to decide wether to build a hierarchy with a Central Administration Site (CAS) or without. Read more, that you can consider if you want to build a CAs or not.
First: You should no what you have to achieve!
Those are the Hard Facts for choosing to build a CAS:
-Number of Devices to manage is over 100’000 (you should know that the CAS has also a Limit which is reached at 400’000 devices)
-If you have to make sure, that a Software package does not leave a specific border
For mostly everthing else, a CAS would be the wrong decision. Remind that a SCCM 2012 CAS is not the same like an SCCM 2007 CAS. The most important Thing is to know, what is globally synchronized data: http://blogs.technet.com/b/server-cloud/archive/2012/03/06/data-replication-in-system-center-2012-configuration-manager.aspx
For placing the Servers (SCCM and SQL) refer to this blogpost:
Hope this helps, Martin.