1. Open source refers to the progamming language the game is written in. The developers have opted to make this project open source which means under the licence people are allowed to download it and look at how it works and modify it and such. The opposite of this is closed source where the program code is not released, such as Microsoft Windows.
2. You need it if you plan to compile (turn the code into a working program). You can compile the source on many different platforms, but you can download already-compiled versions for both Windows and Linux, so no you don\'t need it.
3. It will quite possibly make it worse, because of compilation issues. Stick with the version you have is my advice.
