Japan is pretty hard-coded to go to war with America, barring some ludicrous situation where they are beaten by China. And yes, Germany was supporting China until it became more politically 'useful' to support Japan instead. Soviets and Americans took over at that point.
Speaking of Uncle Joe...well, the Reds are a potential issue down the line.
Italy...we
could end up at war with them, if things go exceptionally poorly with events and such. There's an Italo-German war modeled in the mod, but I've never fired it myself. Right now Italy would have the advantage though since they've got a decent sized army and we...don't. Even with the bottleneck of the Alps and a presumable alliance with Austria. Germany ain't ready to fight
anyone yet, not until I can fire mobilization and build more units.
Also, the German aid to China was a bit more than some advisors:
The German-trained/German-modeled divisions were the elite of the Republican forces.