Just getting a ball to roll is a lot harder than it seems, a lot of your stuff is harder still!
The best way you could do the crumbling effect is to use memblock mesh editing, but that is very complicated. Another way is to make a couple of meshes and switch them when the ball is damaged.
An easier and probably more likely method is to make different textures to use on the ball; turn culling off, transparency on and use black on your texture where you want the cracks.
As for making the balls crumble? No idea
For the AI, have the balls wander around and when near others chase them.
If you are a total noob you wont be able to do all this in time.
I would suggest just trying to get the ball to roll.
Your signature has been erased by a mod because it was rubbish.
