Questions regarding MLAPI multi project setup and the server build

I've just started learning MLAPI and developing a Multiplayer game with Unity. Below are some questions regarding using MLAPI after I've read the documentation.

1. When developing a DGS multiplayer game, are all codes and logics are exactly the same for the client side and server side? (Is it the same project in Unity but just different build modes?)

2. I've seen a concept as "multi project setup" in MLAPI's documentation, what is this? Does it mean that the server side and client side logics can be separated into different projects and have different codes and logics?

3. If we can separate the server codes and the clients as different projects, but some of the network codes still needs to be the same (for example, some network object/variable settings), how to keep them synchronized between the server project and the client project?

4. If the server build and the client build shares the same project codes, is there ways to minimized the server resource expenses as it doesn't need to render the graphics and doesn't needs the assets used on the client?

Thank you very much!