A. Natrualy Imperialistc? Maybe in 1940's, nearly 60 years have gone by. To prejudge an entire nations behavior based soley on history is naive.
B. Agreed. Most, if not all of the electronic parts the US uses for its weapons systems come from Japan. The F-22 Raptor, the US's new 5th gen strike fighters, new avionics system comes right from Japan. Not only would Japan be able to quickly militarize using its domestic industry the US would be happy to sell it its own tech as its doing now with the F-22 and the F-35.
C. Again true. The entire country is run on nuclear power so there is no shortage of fissionable material and with their ability with robotics and fine manufacturing they could easily build nuclear weapons very easily.
D. I totally disagree with you here. Japan may be entering a new nationalistic period, but remilitarizing and going on to pull the same shit they did pre-WWII isn't going to happen. Japan is looking for a permenent seat on the Security Council in the UN and looking to impove its standing on the international stage. Invading other countries with the intent to occupy and colonize them hurt both of those causes. And Japan "bullying" China is impossible. No matter how much Japan builds up its military it wouldn't be able to do much to China. You have to remember that China has the world's largest army at 1,700,000 the worlds 2nd largest air force and navy at 3,520 and 230,000 respectivly. Japan bullying China is out of the question uless they develop working Gundams
E. Again no, what resources would they be competing for? Oil? Remiliterizing would increase Japan's need for it but they aren't hostile with Venezuela or the OPEC nations like the US is so that wouldn't be a problem. Neither would nuclear material for the reasons stated in C and that the US has its own large deposits of Uranium.
F. Maybe no, maybe yes. Its in China's best interest that a communist power stay in control of NK. They wouldn't want Korea to be united under a democratic regime with US troops right on the border or they're own citizens deciding its time for a regime chage of their own, and they sure as hell don't want any poor NK refugees pouring across their border. But they may decide that Kim Jong Ill isn't the right person to head that communist regime. If China does invade NK to remove Kim then they look good to the US and the rest of the world while keeping the status quo in place and securing more influence in NK mostly among the poor.
That and the international backlash of invading Taiwan with no provocation or reason other then for "national unity" looks really bad. Don't underestimate China's military forces if they did decide to invade Taiwan it would be costly but they could do it US forces or not.