After you identify the applications you are delivering to your users and their methods of delivery, you can estimate the number of XenApp servers required for your deployment.
For applications virtualized on the server, the number of servers required depends on the following factors:
Using this data you can roughly estimate the number of servers to deploy in your test farm.
After setting up your test farm, use Load Testing Services on the XenApp servers to simulate how your users run applications on your servers. With Load Testing Services, you can track a variety of Perfmon counters, such as Total Processor Time, Thread Queue Length, Memory Consumption, and Pages Per Second, to determine the resource limits of the servers in your environment. This will help you determine the number of servers to deploy in your production environment.