Moving from a two server Exchange 2010 setup to a four server HA model

Been reading up on this somewhat and from the information I have found, to have HA for exchange in our set up we will need two CAS/HT servers using Windows Network Load Balancing and two mailbox servers in a DAG. I have not gone into any tiny details yet as I have never added new servers to an exchange farm before once it is all set up but if anyone has any similar experiances and knows of any small details that are big deals and can share that would be very helpful.

If you're going to use WNLB for the CAS servers, then you can't have the mbx role on the same server, therefore will need seperate servers for your DAG nodes.

Create a CAS Array, then decide of you want to use a WNLB or a HLB.