Quote: "Could you theoretically make the ground, sky, characters, etc... just by manipulating crap tons of objects like boxes and whatnot?"
Why would you want to do that, just download a free modelling program, theres plenty out there that are free and will do the job soo much better than this. Even if you did manage to make all of these things just with GDK commands you will get nowhere near the quality you will get even if you arent a great modeller not too mention the animation needed to make a high quality game like this will be impossible to doo