Spagedy,
good explanation from dpc but even a better suggestion to get and EE to help you.
I always appreciate other disciplines showing interest in electrical but to do this right you need someone who knows what they are doing to get things right.
In regards to your question however, DPC explained it well and I would just add to it that all loads have to be reflected in the panel schedule as to what they feed (i.e. circuit 1 is it a 20A, 1pole of 15A 1pole or something else, what load does it feed and in what room). Very imporatant and to reitarete DPCs point the loads have to be balanced to the greatest extent possible. When calculating the final connected load you have to apply the sqrt(3) meaning divide the totatl kW by (208V*sqrt(3) or 360).