Is it generally best practice to have a single Document Center for a company, with various Document libraries for different areas of the company, or create multiple Document Centers, perhaps by department?
this will depend on the amount of data and members of your organization,
but as a best practice you'll want to create at least a site or site collection for each department and possible a subsite for each team on each department.
Both of them can be deployed in this case , but before that ,you should compare and consider which scenario is suit for you .
Multiple Document Center :
Advantages : Let each department manage and store their own files and policies , much safety .
Disadvantage :It very hard to manage for an Administrator .
Single Document Center :
Only 1 site to store all files and items , much easy to manage .
For End users , they also prefer going to 1 place to find all your company policies , It is like one-stop-shop!
Disadvantage : If your organization are very huge , different department have own policy and be treated as departmental confidential , it is not very safety .