How do I calculate what size stepper I need (no replies)

So I am building a larger printer. And I am using 3 long 640 mm 16mm rods for a "Y" axis with 3 long pillow block bearings to go on the shafts. Those blocks will be moved by a motor. That is the "Y" axis. The block each weigh about 10 oz and the shaft each weigh about a kilogram. The rods are not moving for "Y". But mounted on top of the "Y" will be two more 590mm by 16mm rods with two more pillow block and another motor to move the "X". So I don't know how to calculate the size of the motor I really need.

Is there a calculation based on weight for linear movement ??? I know it should be each to move it but slow it down and jerking into a different direction could be an issue.

Thanks Steven