You will also need to decide which instances you will need where (usually at least one of each for all levels of testing):
This instance presents the website in its published form for access from visitors.
Should be tested in conjunction with the Dispatcher.
Finally, the actual hardware must be considered - any performance tests should be made on a system as close in configuration to the final live environment as possible. For this reason, it is also recommended that the Project Launch be split into a:
Reduced availability; which allows time for performance tests, tuning and optimization under realistic conditions on the production environment.