There are many disiplines involved with designing a CNC system from scratch, to speed up the process, decide first what you want to do with the table, work wise, with this in mind see if you can see some tables already doing this kind of work, especially industrial types, to get an idea of design concepts.
This will decide the mechanics, rigidity etc, once you have a rough design for this you should have an idea of the weight of the moving parts and this, coupled with the rate of accel/decel and any side forces etc will determine the size of stepper/servo's.
To get a feel of what is involved here, load your designed system into a sizing program like Kollmorgen one etc.
This will give you an inkling into how load inertia at different speeds and acceleration rates affect the size of the motor.
Due to the different characteristics between steppers and servo's, they both require a slightly different approach due to speed/torque limitations when using stepper motors.