As others have said, updates are the 2nd Tuesday of the month. They only come out sooner when it's an emergency.
I believe in the updates, no doubt. Many a compromised system have been fixed by patches that came out a long time ago, but some don't feel the need to keep their systems up to speed.
Over time, the OS is going to simply get bigger as more patches come out and additional pieces of software are installed. If your OS drive is too small, this is going to have a much larger impact on you. Personally, I wouldn't run with a C drive of less than 60GB.