Secret purchase might be fun on the table top, I can see some nail bitters that way haha. Digitally its a little harder to time a simultaneous reveal which is why I figured following the regular turn sequence would probably be easiest to implement there.
In the AA50 1942 scenario it can get pretty wild, since Japan has enough for 4 transports or the option to drop a factory and 2 transports, or pair of bombers and another transport, or probably a lot of other builds. But the Allies also have a few ways to bolster the Russian and British openers, and to get the USA ready to move out a bit sooner. In the AA50 1941 scenario I see Germany and Russia could stack up quite a few tanks against each other, or maybe try to tango with air depending on what G does. Japan has less money to throw around, but they’re all set to stomp anyway in 41, so least it gives the Allies a chance put a few more hitpoints in China and for the Americans to prep for a response. Saving up some of their loot for a major purchase in round 2 is also a possibility for UK/USA if they want to keep the Axis side guessing, or stack drop fleets all at once for a stronger defense, since Axis have so many starting aircraft.
In 1942.2/1942.3 I think 1 fighter 2 art 2 inf might be a nice conservative build for Russia. You could put the ground in Caucasus to ice Ukraine and have the 3rd fighter in Karelia for Sea Lion coverage just in case, but without giving up too much of the defensive edge, since you’d still have those boots on the ground down south. A little more punch each round coming from the extra fighter if it goes more traditional ground war like it probably would, and let the other Allies pick up the slack. For a more aggressive Russian opener you could put two more hitpoints into Karelia to try and snake Baltic states or Belo without it being quite so dicey, and still have enough juice to deal with the Ukraine situation. Or you could try to do like fleet killer stuff in the skies with a Red Dawn bomber play. I think it could be pretty cool.