Test cases for client and server

I am learning a Client-Server Architecture and was developing a system for the same. We have a system for, say 1000 clients, which are sending requests to a Server, which returns them a collection of large number of files. We have some authentication facility for the clients to access the server files. Every client can request only a specific set of files. We need to create Test Cases for our System. My Question:

How do we classify the test cases into "Client Oriented" / "Server Oriented" and what factors to consider to design the test cases?

I figured out some of them:

1. Load Testing
2. Testing if the current resource is being returned.
3. Testing if unauthorized users are able to access the server.

What other test cases may I include for our system?