1. B75 doesn't support caching. But it is not possible even if the chipset supported caching, or at least not recommended... the cache drive should not be the same physical drive as your system drive
2. I think you'll be fine using it for the OS and the main programs
3. Not recommended to reinstall and install all the time. Install all games on the HDD, and if loading times are problematic in a particular game you're playing at the moment, move the game from your HDD to your C: drive using a
junction. This way you avoid reinstalling or installing any game