I have been thinking about my final year project topic and to be honest I want to create something GREAAAT like many others. I know C,C++,Java and Python (Python is getting quite popular these days).. I want to create a small-scale application like Blender (graphics rendering software) any tips for me? I prefer using OpenGL and it's shading language rather than Direct3D since it is open-source. 
Tell me the stuffs I should know to pull this off and also if the combination of python and OpenGL a good choice for this application ?
I want to create a small-scale application like Blender (graphics rendering software) any tips for me?

Yes: Readjust your perception of software size/complexity. I occasionally contribute (TBH, it's been years since I submitted something substantial) to Blender and over the years it turned into a mighty suite. But the codebase is just as large.
Creating small scale application like Blender?