Assistance with a Customer Network Staffing Support Levels

Good Evening:

I'm looking for any kind of industry benchmark data to help me justify IT head count. We're also looking for the same kind of data that you may uses in order to justify IT head count. Things like, How many engineers per device? At what point should the set up internal help desks? Number of trouble tickets per technician, Number of changes per engineer, etc.etc.

Can you point me in the right direction to get this information?

Thank you in advance for any help you can offer.