Questions 1, 4 and 5 depend would depend for me on the results of the battle in W. Russia. Maybe all of the questions would :-D
If you take only 2 hits or less when Germany fires back in W. Russia, you are in a stronger position to try bolder things and get creative. If you take 3 or more hits, then you have to get ready for immediate support to Moscow. This situation is pretty much the same no matter what. Even if Russia keeps the fighters at home, and attempts no other attacks, if G hits big in W. Russia, then the Allies are in a bind. Even a risky perfect strafe into Ukraine can be undone, if the attack into Western Russia doesn’t come off strong enough threaten Karelia.
If the attack into W. Russia goes well, I am partial to soviet tanks and infantry (with support tanks out of India for as long as possible). Or a steady artillery + infantry combo for Russia (and India), with largely air support from the West.
If the attack into W. Russia goes poorly, I favor the infantry wall with concentrated fighter support from the West.
Whether W. Russia goes well or reasonable, or terribly for Allies, might also determine your approach against Japan. And how much hope you pin on things like crazy bomber runs or exposed air attacks. I mean when the situation is dire you might try lots of things to recover.
For question 1 and 2 a med rush or quick transit to the south Atlantic surely does a lot to bring the fight to Germany immediately. And as MarineIguana pointed out it is probably better to keep the Australian fleet alive to fight in later rounds. It is possible to at least bait Japan out of position with it, if you are trying to hammer J. I am not categorically opposed to 37, sometimes 37 can be decisive for Allies with a bid, but its never a given… and it sucks to deal with a second Japanese transport, so there is always that to contend with too. If 37 succeeds it is possible to keep both transports alive, if it fails they may both be stuck.
For question 3, a destroyer locks those subs down. As long as the UK or US has a destroyer, you don’t even need to attack the subs in the first round, since they can be crushed in the second if need be. So subs once used in an attack on 11 are hard to keep alive for G. Its probably better to keep UK transport alive rather than risk it on an early launch, unless you really need the distraction for some reason :-D
4, A British bomber can be interesting for UK, it has more reach on attack than a fighter, but again it likely depends on whether Russia got slammed in the opening.
5. You can go all in on W. Russia, and then decide whether to fully reinforce Caucasus or tank trap it. If Karelia is the focus, it is possible to trade Caucasus if you have to, so long as you have enough force to easily clear the space on counter. Artillery can be very helpful if its your first time out with Russia. Ukraine strafe is high risk, Belo can be the same situation, but even a full stack into W. Russia can get ugly. Still if you concentrate all forces into a single attack, your chances of wiping the space in the first round are increased a good deal.
Whether you play with normal dice or low luck makes a difference I think, to what you might consider doing.