@Argon: You could take a look on the Unity Asset Store. There you can find thousands of assets (models/meshes, source code, shaders, music, sound, and also complete projects). Most of them offer a demo video, or even a playable demo.
Search for 'horror' and you will find many assets for your game project. e.g. this one:
Unity Asset Store - First Person Adventure/Horror KitI think this is a good horror starter kit and a good way to learn how Unity works.
Unity 5 is free and you can use ALL FEATURES(!) of the engine. The only difference between the free 'Personal Edition' and the 'Professional Edition' is the splash screen (Unity logo when starting your game). When you buy the 'Professional Edition' then you have access to beta versions of Unity, and your bug reports will be verified with a higher priority. So I think there is no need to buy the PRO version. You can develop and sell your games also with the free version of Unity.
