A) As for the submarines, part 1 applies. Let the submarines die so your surface ship gets more shots at the British air force (which I view as their navy, given that they are an island.)
B) Given the location of Western Europe, leaving the fighters there makes the best sense. They prevent the British from landing (and the Americans in round 2+) while still being used to pound the Russians. Again, part 1 applies until Japan is in position to take over, then Part 2. 4 Ground units should be fine round 1, but review the board each round and up the defense as needed.
C) In general, keep parts 1 and 2 in your mind and act accordingly to the position on the board. If you need to pull of Russia and start turtling in round 5, do it. If you dont need to until round 7, then dont. But certain things always apply:
1) never let the Allies have Western Europe.
2) Never let the Allies get Southern Europe
3) Is self explanatory, derive from 1 and 2.
4) Geramny’s goal is to inflict damage, Japan’s goal is to take Russia. Not a hard and fast rule, but a good guideline.
5) If you go navy with Germany, you will have to keep building up to keep it. Personally, I dont recommend it unless you are strong with Japan.
6) Tanks are good defenders. I like stacks of 5 or 6 infantry and a tank in forward areas against the Russians. It’s big enough that Russia has to invest heavily in winning, but small enough that Germany can recover the losses. (It’s economics, like the cold war. Spend them into submission!)