Virtualization is typically used to provide workload consolidation, but this means, without the right resource management, just blending everything; this could become a risk, like putting all your eggs in one basket without taking any precautions. Besides, all shared components of your infrastructure will most likely be affected in some way by this significant change (for example, storage or the network). Moreover, standard procedures such as monitoring, backups, patching, and administration will also be affected.
Before you start with the virtualization of the existing physical environment, you should carefully assess all components of the existing infrastructure. With servers, you should focus on the utilization and any potential performance bottlenecks, but you should also assess the other components of the infrastructure...
