Clearly, the centripetal force could not create a spherical shell, since it is nonexistent at the poles. It could only ever create a doughnut-shaped body, like the rings of Saturn. But like rings, such things are typically gravitationally unstable and tend to collect into single, solid bodies (aka, moons).
Regarding his other issues with gravity:
Correct - therefore the calculated mass of the earth could not possibly be wrong. You can't have a hollow gas giant (or sun, for that matter), and we've sent space probes to every planet and many, many moons. Obviously, our understanding of gravity must be correct.
I love self-debunking crackpots!