if you start building fleet early on with germany it will “telegraph” your move to the allies, if they realize what you are trying to pull, they can easily hold uk long enough for russia to take you out (5-6 turns)
The best bet I think is save the initial 12, or maybe save 8 and build an artillary (As you will need one more for optimal odds on uk)
Now, depending on what the allies bid, you can attempt to save all 40 on ger1. Take all uk convoys and destroy all uk fleets, not the med one. Make it not possible for uk to retake any convoys the next turn. Battleship to gibraltar. Turn 2, try to get as many subs with your battleship and destroyer in bay of biscay, two moves from denmark straight. Still depending on what allies buy and what they are doing, you might be able to save again.
All the while get your artillary moving toward germany, so when you build 11 (or 12) transports on germany turn 3, you will have all your artillary in germany. This includes the artillary from africa.
Now, with fighters in range, and ready to load 22 (infantry and artillary) units 5-6 fighters and bomber and bombard, you should have odds on taking uk, and if not, don’t forget wave two the next turn (you can use a few tanks here since you will be low on artillary) This is also for retaking uk to finally hold it if the usa retakes from the first attack.
If wave2 (on turn 5) fails, you will most likely lose. If the allies build significant defensive forces before you build your fleet, build an army instead and invade russia.