Utilization studies are a great first step. Most utilization studies answer the question of how much am I now using, and how much will I grow? These are a standard feature of every AR Consultant Group product recommendation.
As with any study, the amount of data provided can greatly vary. So you just need the basics across your organization, or are you interested in seeing what each application is using in depth and sizing special servers for this? Who may be your super users? How much will you grow over time?