Network Infrastructure

I need a broad scope of recommendations for a class I am taking. I need info on the best way to build a network with these requirements:
– 75-120 users, ranging from data entry to mgmt. in one location
– Email, calendaring
– File storage, file & document sharing, private storage
– Internet access
– Some business apps need server-based db access

Any info will be useful, especially on these topics:
– O/S specifics
– File-System
– Memory requirements
– Security
– Limitations (if any)
– Cost

If anyone can help me with this it would be greatly appreciated. Like I said, I just need a broad scope of recommendations and info.
Thank you.