Mixed reality is looming over all of us as UX designers. It's indeed a robust subject matter to tackle and I don't blame you if you're head spinning. The best place to start is with a simple Google Cardboard and an implementation of WebVR online or even locally. If you really want to get into 3D modeling and stuff like that, you can use tools like MagicaVoxel, It's Free, or Cinema 4D. And then to go big, something like Unity for your physics,. You'll see what's possible when you get an HTC Vive in the near future.