Add another server? System architecture/design question

Hi All,

We are starting up the project to implement FSA in our environment. We currently use EV for exchange (~1000mailboxes + journaling) and DA (installed on a seperate server). Both servers are VMs and are running version 10.0.1.  We are open to the option of adding another server to help handle the load, but I'm not sure how to tell if we really need one or not. Are there performance counters/metrics that we should be watching?

Where do we start?

Thanks!