What we're really missing here is that Japan didn't have the manpower to invade the United States, and even if they did manage to land on the West Coast they didn't have the mechanization to advance far inland.
What Japan really wanted to do was seize Hawaii, the Aleutians, Australia, Fiji and New Caledonia, and then force the Americans to sue for peace (since there's nothing between Hawaii and the US, and launching an attack to re-take Hawaii across the open ocean would have been quite a challenge). Then, they hoped to apply the resources of all the places they conquered to their war in China.