I need to pick up a stepper motor for a specific application and would need to some education.

I have a 5kilo object that I need to turn to turn. It is shaped like a pyramid and will be connected at the tip to the shaft of a motor. The height of the pyramid is 4in and width 10in. What inertia and torque do I need to turn this around shaft?

Below is my best representation of the motor+shaft+pyramid .

[]
[]
[] []
[] [][]
[][] []
[] [][]
[] []
[]
[]
[]
[]
[]
[][][]
[][][]
[][][]
[][][]


At the bottom is the motor with the long shaft coming out of it. The triangle thing is the pyramid that is fixed to the shaft. In our application the motor does not need to move faster than 1-2rpm. The motor will be some kind of stepper motor heavily geared to reduce the shaft speed. My problem is figuring out what kind of motor I need for such application. I guess I need to figure out the torque and inertia required to move the pyramid.

All help is appreciated.