Yes to nearly everything said above.
But I’d challenge you to take it one step further than thinking about specific purchases - think about how those purchases can provide flexibility, afford you to take attacks of opportunity, and keep your opponent off balance. The units follow the philosophy, not the other way around.
So a purchase of a CV/DD/ Sub is about much more than just the math… it is about Germany’s ability to project power in a variety of directions. G2 can be a Gibraltar strike, you can hit Morocco, you can bend to the other side of the UK, hit Scotland, and convoy raid up to 8 IPCs… and keep doing it until the UK forces you off the spot. You could go into the Baltic. On G3, you could flex back up to 112 if you own Gibraltar… or, you could go into the Med to support Italy. It goes on and on.
So take the same approach on land… what buys you the most flexibility? Certainly not infantry or artillery, though they’re necessary at some volume. Instead, make sure to diversify. An example of a potential G2 purchase for me might be a bomber, destroyer, transport, armor, five mech infantry, five infantry. A few infantry to defend the coast, a few infantry to serve as fodder in the fight for Moscow, and a whole bunch of versatile mechanized forces to form an armored fist on the front.
If you keep diversifying, you find yourself capable of handling just about anything the Allies throw at you, and you can throttle Russia at your leisure. If you become too monolithic, too predictable, it allows the Allied player to easily see your weakness and exploit it.
I will take your advice to heart.