You’re asking good questions! Glad you’re having some fun with the game.
I think you’re right that the out-of-the-box rules tend to reward a game that happens mostly in the Atlantic/European theater. It’s not too hard to fix this with a bid or a house rule. For example, you can start Australia off with a factory and start with Wake Island under Japanese control. That means the Americans have to conquer a Pacific island somewhere in order to collect their national objective…which means that the Americans effectively have several juicy 5-IPC targets at the start of the game. Note that there’s no need to burn the Australian factory; even if the Japanese take it over, they would almost never want to use it.
Another way of looking at this problem is to just…play differently. Like, yes, the European strategy is probably optimal. But the Pacific strategy isn’t that much worse. If you’re having an easy time taking German territories and a hard time taking Japanese territories, then maybe you want to try something a bit different and focus on taking Japanese territories. What feels “easy” is often a matter of how many resources you’re devoting toward the task.
When I play Germany I usually transport at least one load of troops to Norway, two loads if I can get away with it, so that there are 8+ Axis infantry in Scandinavia. Once Germany has firm control of Leningrad, the British presence in Norway is not so bad, but early on Germany needs the income.
Building a German navy is fine within reason, but you have to know where to stop, because ultimately the UK + US together can outbuild you in the Atlantic and sink your navy at a profit. You can’t permanently win the Battle of the Atlantic against a competent opponent, so you shouldn’t try. But 1 carrier can be an excellent purchase because it keeps your Baltic navy alive for an extra two turns or so, which can be the margin of victory in taking Leningrad and holding Norway, so it sort of pays for itself even if the navy eventually winds up on the bottom of the sea. It’s also fine to build no German navy and just focus on blitzing Russia.