I was trying to simplify the question and therefore wasn't clear...
Art 220 is a big help, of course.
My confusion I think is that the initial loads are small, so I don't want to terribly undersize my service.
So with, as in my simple example, let's assume each 100A panel and transformer has a connected, let's say continuous, load of 30A.
30 x 1.25 = 37.5A
37.5A x 4 = 150A.
So I could use a 150A service to comply with 220. But that leaves no room for future growth. So maybe I'll do a 300A panel.
My question ultimately is, when future growth is unknown, how do you decide?
Thanks,
JM