Nate,
To elaborate more on your 2nd and 3rd questions;
* Clustering is not just connecting all ESXi hosts together, but its another means to aggregate all the compute,memory and storage resources together to leverage vSphere features like vMotion, FT, HA, EVC etc.
* Get a brief idea about which VMware feature protects planned and unplanned downtime of your servers here
* vMotion is a feature which ensure high availability of the VMs. But to vMotion VMs across ESXi hosts there are some prerequisites which needs to be met.
Refer the <link> for more info.
* To know more about hardware compatibility with VMware products refer <link>.
* Access the product documentation for latest vSphere version here
~dGeorge