Sparkynyc,
Do you guys, not have Maximum Demand Calculations, in the US?.
These give the fact,(called Diversity Factor),that not all of the loads will be drawing current at the same time.
We use these calcs, to size Mains and Sub-Mains, over here in New Zealand.
These Calcs, can also be applied to Gen-Sets
too, as they are the same as a Mains supply.