What are the average APC attack levels needed to defeat different levels of zombies and rebel camps..

There isn't a list for this but when you tap on a zombie to attack it will have a statement along the lines of 'Come challenge when your combat power achieves ...' If your APC combat power is at or above this then you should defeat them (although the closer you are to the level the more losses you will have and the chances of winning are reduced). If you are below then you will be more likely to lose or at best, win with heavy losses.