I would do Belorussia with THREE USSR infantry, not two. Three is far safer. If you lose two infantry and the Germans lose two (moderate possibility), you must retreat as the move stands. With three USSR infantry, you could challenge Germany for that territory and possibly get the 2 IPC territory as well as killing the 3 IPC German infantry without endangering your 10 IPC fighter.
Variations of your build - I often move the AA gun from Russia to Caucasus. The German bomber can’t reach Moscow without leaving itself vulnerable to a counteratttack from West Russia. Also, I’ll sometimes opt for two infantry two artillery two tanks, place infantry and artillery at Caucasus and place tanks at Moscow to threaten a Ukraine attack/counterattack next turn.
You can use the open-Caucasus version later in the game too. If Germany’s navies are destroyed, or too strong to attack, and you have plenty of fighters, the bombers will probably not be optimally used. So you can leave Caucasus open, wait for the Germans to take it, strat bomb with UK and US bombers, retake lightly with UK/US/USSR, and repeat. If Germany takes the Caucasus, they actually LOSE IPCs on the trade. If they do not take the Caucasus, they will still have a harder time dealing with USSR because USSR didn’t have to mass at Caucasus (USSR masses only at W. Russia, which slows the German attack).
BUT with that, you have to watch for two things. First is if Germany takes Caucasus, and Japan flies fighters in for additional defense. If the Allies counterattack Caucasus, Germany might be able to counter-counterattack from Ukraine, and things get dicey. Second is that bombers are powerful units that are almost certainly better used to swing the balance of naval battles in the Allies favor. So the open-Caucasus mid-game variation should probably NOT be used in most games.
The usual German counter I use to Belorussia/W. Russia to attack Karelia in force; if USSR attacks heavily from W. Russia, they are overextended, and I’ll use German air plus ground to crush the mass of the USSR forces. I also counterattack lightly in all the territories possible - usually Ukraine and/or Belorussia if applicable. I use the German navy to wipe as much UK navy as possible. If I had an African bid, I’ll unite the Med fleet and Atlantic sub so I can make for a better German Med fleet or unite the German navy on G2. I always smash Anglo-Egypt under the given circumstances described.
In your described variation, I would attack on the heavy side because of the noncom movement of USSR infantry east - I would probably look to see if a massive W. Russia crack w/ German air was possible (because Russia’s counterattack would be limited to infantry and fighters). Of course, you take into account the fact that the Allies will consequently have a better naval position relative to Germany than otherwise . . . and that Anglo-Egypt might not be cracked, etc. etc.
If USSR moved poorly (in any game), I may sometimes attack heavily into Caucasus, but that is VERY rare; if USSR placed fighters at Caucasus, I may build Baltic transports for a threat to Karelia and London, etc. etc.