my question is if i were to hollow out my stock catylic converters will it set off my check engine light cause of the o2 sensers? And also do i need all four of them?
yes it will set of the light. its not worth doing it will only harm performance and sound. the hollow chambers will create turbulence in the exhaust and hinder flow. if you want performance and sound gains invest in some mid pipes. the mid pipes can be either catted with only two cats or o/r with no cats.
Just buy a better midpipe without cats and you'll be much better off. I strongly recomend the mac prochamber i noticed a significant gain in power and sound when i put mine on.