如何将Objective-C（iOS app）代码分解为面向对象的设计

I'm starting a massive project for the first time. I was supposed to be one of the developers on this big project, and all of a sudden, the lead developer and his team backed out of the contract. Now I'm left managing this big project myself with a few junior developers under me and I'm trying to get a firm grasp on how this code should be broken up.I'm starting a massive project for the first ti