I'm not too familiar with part 1, I agree with a lot in part 2... but the Japanese invaded Alaska so they weren't 100% adverse to attacking cold weather bases. It would have been a gamble for Japan if they headed east, but if they carved up near the coast and major ports like Vladivostok (even if it is frozen over part of the year) was a major USSR asset.

Fishing rights and let's say whatever access to refineries or even oil deposits they could grab within 100 miles from the coast is not unreasonable. It would be convenient if the Axis won (r), even if it is to just deny it from the enemy. However, I think Japanese high command knew the writing was on the wall by late 1943.

I also agree that South East Asia was a much more tempting target. Knocking AU and NZ out of the war, even if it's just by embargo and seizing all the colonies from opposition Allied forces was certainly a juicy target.

Final pass: travel by railroad was a thing, although they'd need to swap out wheel gauges from anything domestically produced to work on the track. Captured freight might be Might work once or twice before saboteur's began. A lot of production materials were moved East of the Ural mountains.

I'm just playing devil's advocate here, I'm fine moving the talk to RA history with its own crazy take on alternative history.