Q: Is it better to have one large 64-node cluster in Windows Server 2012 or have multiple smaller clusters?
A: There's no right or wrong answer to this question. The nodes in a cluster have full ability to share resources and to move resources between the nodes. Thus, the larger the number of nodes in a cluster, the greater the ability to consolidate and share resources.
This leads to less waste and allows the number of "spare" hosts to be reduced. Additionally, Windows Server 2012 has capabilities such as one-click updating of an entire cluster, so the smaller the number of clusters, the lower the amount of management overhead.
The opposite argument is that a cluster is still a single cluster configuration, so in the event of some very severe cluster corruption, all the nodes in a cluster would be unavailable. Because of this, typically people will at least split resources into two clusters; remember, in Windows Server 2012, it's still possible to move virtual machines (VM)s between clusters without downtime.