The toughest thing for Japan is resources/factories and maintaining a large Empire that stretches from the mainland to China and beyond.
As Japan your safest bet agains the USA is a large capable Navy. As players we have the benefit of hindsight, but Japan saw this too. By investing heavily in carrier and aircraft technology that will give the edge Japan needs to keep the American's at bay.
- Build lots of smaller carriers, I am thinking Tier I or Tier II.
- Retrofit and build as much as possible.
- Small but efficient land force.
- Land focus should probably be aimed more at Infantry (and/or Marines), with a small to zero focus into armor.
By building many Tier I and/or Tier II you will gain a build speed bonus by not switching to something more advanced. Additionally you will also have an edge when you start getting experience from combat and can otherwise improve these older designs. By having many older models it will allow Japan to be more spread out. As opposed to having larger fleet carriers all focused in one area. Expanding the navy should be paramount. I would have to expand the dockyards to about 20, have two sets of carriers being built as quickly as possible (6 months or less) and additional screening ships (cruisers, destroyers, etc). It may be good to invest 1 or 2 dockyards into Sub's (depending on "how" useful they are) for naval interdiction purposes. Unfortunately probably no new battleships.
Due to the large amount of island chains, you are going to want to invest heavily into an airforce to compliment Infantry/Marines. Armored warfare will be secondary and probably a focus for much later in the war. The island chains are a strength and weakness. You can [probably] gain high defensive bonuses and by focusing on infantry/airforce make it a daunting task. But at the same time being spread out can seperate armies. Having a decent airforce stationed at every island chain and good size garrison of infantry/marines will help ensure the defense of these islands will cost an enemy a lot of resources to take it. In addition to a land based airforce, being able to have many smaller carriers allows you to be more mobile with aircraft and hunt enemy ships that would aid in the invasion force.
The USA has a huge industrial capacity, but it will take time after Pearl Harbor for the USA to get into full swing for war production. Japan NEEDS to be prepared to take on this beast in the Naval arena, and they have about a year after Pearl Harbor to do so before the American factories and dockyards start churning out.
After the Hawaiian islands, and Alaska falls. Japan will be hard pressed to make a move on the mainland USA and Canada. By this point Japan will have a sizeable industry and military built, but as a result of over-extension may find itself vulnerable pressing further. Realistically I would sue for Peace with the USA depending on how Germany is doing with the War in Europe, if they are doing well then invading the US/Canada may make sense. If they are in a stalemate with the UK or start suffering due to a "D-Day" type invasion of France, Japan will have to start a large interdiction campaign against the US. Focusing primarily on Panama and any South American Allies.
China (and eventually the USSR) will be an issue. Japan should be able to annex and defend China, especially in it's mountainous terrain from most advances. But depending on the USSR's stance during the war if they decided to make a move it could break those defensive lines (depending on their commitment).
My 2 cents....