Capacity Planning

I have just joined a netwprk capacity and performance department,
Dilema: there are no documented standards or matrices on Network capacity planning, we have a powerful that is being used for adhoc planning.
Question: what industry standards,considerations and methods, besides reading reports should one employ?
Dilema: The organisation I work for has numerous(over 20) in house built and other applications.
Question: what is the best way to identify and profile these applications?