As Osso said, you don't need an I-beam. I only mentioned it because a contractor might use it. Wood will work just fine for temporary support.
4x4 columns are probably fine since they were used the first time. The problem isn't the 4x4 post. It is the way the post was supported underneath. The building inspector can help you out some. He isn't going to want to do all your calculations for you but he does it enough he can give you an idea of the right way to do it.