The key to playing well is to not try to force the game to fit general principles, but to find the right general principles for the situation.
That is the first law. Everything else is just a matter of identifying general principles, and knowing how to distinguish when using a particular one is appropriate.
The second law is to remember that the balance of power is very tight. A couple of units one way or another means a huge difference in win/loss percentage.
If you apply the first law to the question of the G1 build, it no longer becomes merely a question of whether or not ten infantry and a fighter are a good idea. It becomes a question of when ten infantry and a fighter are a good idea. (never? sometimes? always? and if only sometimes, then when?)
If you’re going to build German air, your best payoff comes if you use it to control Allied access to Africa early, while pushing for quick PU income gain in Africa. The scenario is something like G2 in Anglo-Egypt, but preventing a UK2/US2 landing, then you follow with G3 movement through Africa.
But if UK builds a fleet on UK1, you can’t really prevent a UK2/US2 landing; the combined Allied fleet will just be too big. Even doing a G2 submarine build at Southern Europe is usually not a good Axis answer because you pump all the income you get from Africa into the subs, the subs are easily trapped in the Mediterranean, and UK can just land in Europe, plus US can afford to build fleet to counter, so effectively Germany loses out.
So often Germany will build even TWO bombers, or a Baltic carrier, to threaten the sea zones around UK. (But a Baltic carrier is another matter entirely from the OP’s subject so I will not elaborate).
If you just build a single G1 fighter, you usually won’t have good odds on wiping out a UK1 fleet build, meaning a possible UK2/US2 landing at Algeria, and less odds of holding on to Africa territory for a while.
Still, you will probably land all fighters at Western Europe. Even though the Allies can unite and land at Algeria, landing at Algeria in force means no landing in Europe, allowing Germany to maintain control of valuable Norway longer and generally allowing Germany to press Russia longer in the early game.
But maintaining German fighters on Western Europe is a pain. If you keep fighters on Western Europe, they can’t really lend their power to attacks in Europe. If you move them off Western Europe, then you lose the threat to sea zones.
So usually German fighters end up somewhere else.
Later on, you may have two fighter bases; one at Western Europe, and another at Eastern Europe. The one at Western Europe will be to bolster the defense of Western Europe, threaten various sea zones in the Atlantic, and to trade Karelia. The one on Eastern Europe will bolster the defense of Eastern Europe, threaten the Kar/Arch sea zone, and trades with various territories like Belorussia and Ukraine. The fighters on Eastern Europe that hit Belo/Ukr targets can end up back on Western Europe; the fighters on Western Europe can hit Belo/Ukr targets and end up on Western Europe; this way Germany maintains a huge threat range with all its fighters.
If you can do it, it’s nice to establish firm control of Karelia for a turn. After you maintain control for one turn, you can land German fighters there, which threaten off Allied navy from immediately reinforcing Kar/Arch/Norway/etc.
Axis air builds and Africa go together.