a). Yeah, MarkA, maybe you mean, "minimal effort" as in OTL but ITTL, the Japanese would have committed a great amount of military force in taking the PH, resulting in larger, bloodier and more signifcant East Asian thatre for WW1 with the Japanese of course playing a much larger role. The Australians would probably join the Japanese in taking the Philippines by fighting in its southern parts and like I said, the British would get that part of it after the war and the Japanese would get to take the remaining 2/3's of it.
b). If you look at the history of the Far Eastern Republic, the shortlived Siberian state. (
http://en.wikipedia.org/wiki/Far_Eastern_Republic), you'll see that it was created with the tacit support of the Reds because of the desire for a buffer state between Red Russia and Japan. Now, a number of consequential events such as coups and defections, that easily could have gone differently, caused it to voluntarily join with the USSR. And if things had gone differently, the Japanese could have lingered on for a much longer time, even without maintaining a major military presence there and by just having close relations with the FER as an ally or vassal.
And its just really the Japanese discovery of oil around these parts that is the main POD so things could go as in OTL with Manchuria falling to the Japanese around the same time or earlier and then oil being discovered.
c). Also, you have to remember that all of these POD's happen in the same TL so its a combination of all these things that really makes for the Japanese victory. Also, Japan isn't really threatening US interests, it mostly focusing its might inland into mainland Asia rather than in SE Asia and the waters surrounding the US. Now that it has resources to take China, it would have no reason to do most of the other things it did OTL. Maybe it could go on to conquer the rest of SE Asia (it already has the Philippines) much later when it is more powerful and when its occupation of China has been consolidated.