Check into the Microsoft Operations Framework for some ideas on this activity. See the WhatIs article for a brief overview.
A couple of other good places to start are:
- CMG– an organization that’s all about performance and capacity planning for all platforms.This site has some great presentations and articles.
In a scenario like this. I would suggest approaching your primary vendor. Letting them figure out some options for you. They have other customers, who very likely have been through the phase you are in already.