didn’t have time to read all of it, but one thing that has probably not been mentioned;
when germany is capable of taking moscow, then, it is time to retreat, if you alow his stack to kill you in moscow, and then turn south, it is hard to defend cairo, if you retreat from moscow, and force him to keep his stack there, then that stack will not turn south. at this point you will prolly only collect like 8 ipc anyways, while your army should be worth at least 250 IPC, prolly like 300, do not let him kill it for half the number of IPC, then it is far better to let him get moscow, and keep retreating, forcing him to either build a completly new army to attack cairo over land, or to alow you back into moscow at some point.
