Excellent moves. I do agree that this seems to be the best route of attack for you in your game. That Rader left such a vulnerable gap in his defenses is probably a sign of two things that have been pointed out earlier (especially by Nemo). Rader is not a great player. By that, I mean, he is an excellent and experienced Japanese player that adapts fairly well and had a good game plan, but even with basically every advantage possible (India and China, massive acceleration of his aircraft development, intact kb, etc) he seems to have been fighting the last war (against jzanes) instead of the current one (see buildup of timor, massive acceleration of fighters (presumably to counter 4e bombing, fighting harder at the Solomons to delay the push longer). This is not the sign of a great player, but merely a good one. The other thing is that Rader tends to overcommit to everything it seems. While I certainly think he should have had glen equipped subs as pickets along that route (there's a very wide, hard to scout gap in islands that an afb can exploit, especially if midway and the aleutians are not Japanese scouting bases, or subs and pickets deployed), I'm not sure that even an extra week of warning would have been enough. My guess based on his play is that most of his shipping is commited to the evacuation/repositioning in new guinea and the reinforcements to the DEI from elsewhere. That Australia buildup was an excellent maskirovka for someone hellbent on fighting at the farthest perimeter as long as possible. You played him like a fiddle in the hands of a very hairy hillwoman. I would be completely unsurprised to find he had nothing resembling a strategic reserve within a week of the home islands at the time of this invasion. I do also think, as I said earlier, that even capturing the DEI might not have been strategically significant at this point in this game, so your move to a strategically important (if not decisive) AND vulnerable location was very wise from my perspective (and obviously from your better informed (and probably with better reasoning) perspective, as you executed it well).
That said, your losses early on have probably been to your significant advantage as a player. You learned very quickly how passive play gets punished, and you were forced to consider unconventional thinking to counter his swarming defensive across a very, very thick perimeter. Keep this up. Your losses forced you to learn deeply and quickly or lose totally, while his successes seem to have given him victory disease.
Keep in mind Nemo's invasion of Okinawa in his aar and the vast Chinese and Indian divisions now freed for use in the home islands. I wouldn't consider it an overreaction at all to send every last available division to reinforce your holdings here (as you really do not need to push your perimeter any closer unless you actually invade Japan). An unconventional counterinvasion could make your life more difficult, so making each base untakable to any size landing in the short term (with adequate strategic reserves to guarantee a stalemate in the mid term). Obviously you'll suppress the eastern kuriles, but I do not think it would be a mistake to conquer them in the timeframe 6 months out to further your hold. Committing all your forces to a single axis is fairly easy to counter, but if you're already deep into his strategic depth (which can't really be moved out of the home islands in this case), you can guarantee the war. Stalemate isn't good enough for him here, as you're too close to his vitals. If you still have any doubts about his plans (and I personally doubt he has the psychology to really try), if you put everything this axis at this point, he can't kick you out even with everything he has committed to a brilliant plan, imo. That's almost certainly being far too conservative, but given how the game started and what a big gamble you took to get this position, conservative play to secure it (at least for now) seems to be worthwhile (and your plan, as you indicate). But hey, sometimes it's comforting to hear other people suggest to us the things we are already thinking.
All in all, gj gj.