On Hitler getting shot: well, your call. But Nazi Austria would be great

. Maybe use some other Nazi leader..
On SU targeting Japan: spot on. Historically, in 1938 it was a conscious decision for SU to concentrate on Germany. For a moment there was discussion about who is the main potential enemy of SU - Germany or Japan. In this timeline, it would be Japan. However, if full-scale war would happen in 1938 with Japan or some time later after that, Japan should be very much defeated by Soviet Union. So, even if Britain would declare war on Soviet Union over this (I think it shouldn't.. too far from history), Manchuria would still probably get a communist government & become Soviet puppet (I doubt Soviet Union would occupy and annex Manchuria, though, there's also chance of that). But war would probably end with that - Soviet Union *maybe* might also go for Korea, but its a less likely chance. After proving to itself and the world that it can beat the Japanese, I assume Stalin would get overly ambitious and push Romania to give Bessarabia (in ~1940-1942?), after which or because of which then he would decide to use some excuse to attack Poland (historical Polish-Romanian alliance of defence would probably be in force here). Britain and Allies would probably try to give guarantees to Poland and Romania, however, if historically Allies had technical and motivational troubles defending Polish western border, imagine how bad it'll be with Polish eastern border.. So, it would be too much to say that Allies would defend Poland, if only Poland would be attacked. But, Stalin would probably use the time while Allies are barely mobilizing and attack Poland, Romania and India at the same time. Since, getting influence or control in India was a part of Russian and Soviet foreign policy, then, thats how the world war might begin in this scenario. And, when Poland would fal, I assume that Soviet Union would attack Baltic states and Finland, after which, it would be time for Germany. Actually, Democratic Germany might also join Poland in defense if Warsaw would fall.
Also, about Nazi Austria - I'd suggest having it, because that would be the way to have some kind of Axis in this mod. Otherwise, Axis would be just Italy and/or Japan? By the way, to strengthen Axis, maybe Italy and Japan should have closer cooperation between themselves, and have alliance from the start, thus joining each others wars (which would probably be, without Nazi Austrian conquest wars, just two - Abysinnia and China). That way they would be slightly beefed up and stronger. Though, realistically speaking, Italy and Japan had only very limited possibilities to wage war across so huge distances.. and very little political reason for that as well. However, since in hindsight we do know they'll need each others help, then why not.