When considering a handling system of any type, always work from the end effector (gripper or vacuum) upwards. Firstly size the gripper, then any rotary actuator requirements. After this, size the vertical (Z axis) and then any horizontals (X and Y axis).
If your requirement is for a multi axis solution, the best practice is to reduce the amount of bearings between the rigid frame and the product. By keeping this to a minimum (5 bearings absolute maximum) you minimise the cumulative deflection and therefore improve accuracy. Also, if the axes are electrical, problems are compounded as high play and deflection effects the tuning of the axis and produces an unstable system.
When considering mounting servo and stepper motors on to mechanical axis, ensure you allow for misalignment. Flexible couplings such as “Oldham”type or bellows, couplings are ideal.