Did anybody mention that San Andreas was only around 3GB? Fits pretty well onto a DVD9, don't you think?
No tutorial. Just put all of the instructions into the instruction manual and very subtle hints during gameplay, that should stop appearing after a short amount of time.
EDIT: Besides, you learn faster if you jump right in.
And Oblivion was 6GB, and there is no way in hell will GTA 4 be bigger than Oblivion.