Q. Do I need to create a separate SharePoint area for each team? Or can I have one SharePoint site grant access to each area?
A. Depending on your access needs and the desired end-user experience, you could have just one site and assign access by list, library and even folder and document.
Keep in mind that if users find it difficult or confusing to access their data on SharePoint, they will look for local storage solutions on their computers. SharePoint helps by only showing what you have access to. For users with broad access permissions, pages may get messy. This is particularly notable with multiple team calendars. Make sure you consider ease of administration along with end-user experience when deciding.