You should organize your project in a way that preserves the logical separation of concerns in your application. This makes it easier to share the project among teams working in the different tiers and makes it easier to find source files and other assets.
Your source code, tests, automation scripts, and other application assets should all be under source control. Source control preserves historical changes to your application and enables multiple people to work on a project concurrently. Putting all your application development and deployment components under source control also makes it easy to know goes into each release of your product. Even a the smallest team benefits from source control.
For example, if you move your testing infrastructure to a new host, you should only need to update a single configuration file, not every test. Similarly, you should be able to change product build dependencies with minimal configuration file changes.
Project development involves many repetitive tasks. For example, a developer goes through the edit-test-debug cycle many times in a single day. Automating common tasks improves productivity and reproducibility.
Similarly, using automation to simplify testing removes barriers to frequent developer testing. Frequent testing improves product stability because problems are easiest to diagnose and fix close to the point at which they're introduced. Test automation also helps improve the reliability of test results.
Automating the setup of your application development and deployment environment makes it easier to add new developers, manage dependencies, and provide a stable development, testing, and release platform.