You can take the doors off legally (with rear viewing mirrors as described in link above) because the vehicle came from the factory with that ability. Safety (what it is) was designed into the vehicle as to provide whatever safety is required to sell the vehicle.
I am pretty sure that removing the roll bar would negate a safety feature and might be illegal.
Personally, I would not want to drive my Jeep without the roll bar on or off road. If you roll, you are probably dead. And Jeeps are not exactly ground hugging vehicles.
As far as the windshield.....not sure about that one either.
p.s. Regular convertibles have to pass federal standards for roll over, the windshield is part of that safety system.