This is not an easy question, because it depends on a multi-turn strategy that does not exist in a vacuum from distractions or opportunities of the game. You also explicitly said “driving” there. With that in mind, here’s an ultra-conservative direct push towards Moscow.
It is exceptionally useful to have some Italian fast units come eastward with you to take empty territories or territories with only one Russian in them so your planes can land on your main stack as it marches east.
A careful Russian player will punish you for mistakes by killing pieces of your invasion force if you split it up. Take extreme care to not let him outmaneuver you like that, as it’s usually the first dozen nails in the coffin all at once for Germany.
G1:
This is complex. Let’s assume no G1 Barbarosa, which is not a “standard” tactic. If you want to do a Sea Lion feint, then you can buy a navy here, or spend nothing at all. If you instead build a bunch of land units, then UK can do whatever it wants on its turn and you’re telegraphing your intentions to everyone. Generally, I’d suggest getting some navy or to save your 30. (The navy can be somewhat useful for moving some dudes in the Baltic against Russia, too.) If you give no shits about telling Russia/UK what you plan to do (very risky), then buy 6 artillery and 2 infantry.
G2:
10 artillery in Germany. Five turns from now these will be attacking Moscow if the allies let you. Buy whatever other units you want out of western germany, be they planes or tanks or whatever “fast” units you feel you need to kill Russia later or support whatever other thing you’re doing right now. You can declare war here provided Russia has left you some units on the front lines to kill, or you are confident you can make it to Novgorod with little resistance.
This is the absolute last time you will every buy a “slow” unit, unless it’s on the western front to counter some small, weird allied landing parties.
G1 buys, if any, move to Poland.
Victorious tanks from the French campaign (and mechs unless you need them to kill Normandy/Southern France) move east to Yugoslavia.
G3:
Buy tanks/mechs (heavily favor tanks). Planes only if you need them. You can declare war here provided Russia has left you some units on the front lines to kill, and G3 tends to be the “standard” time to get the ball rolling.
Starting units (and perhaps a G1 buy) that were grouped up on the front go to Eastern Poland or Baltic States depending on whether you’re moving the bulk of your force through the south or the north. Both have their advantages. I prefer north most games. Wait in Poland only if you absolutely must.
G2 artillery to Poland.
French campaign veterans East to Eastern Poland, and they are now with your front.
G4:
Buy tanks/mechs (favor tanks unless you’ve lost a lot of mechs already). Planes only if you need them. If you’ve not already declared war, for god’s sake do it now.
G1&G2 artillery eastward. You’re either 2 or 3 spaces from Moscow with your front, and your G2 10 artillery are either with the front or one space behind.
G3 tanks/mechs eastward to wherever your G2 units are, 3 away from Moscow.
Bomb Moscow if possible.
G5:
Buy planes. Whatever optimized combination of strategic bombers + tactical bombers you can. You should own Novgorod or Ukraine by this point (or both if Russia sucks).
G1&G2&G3 combine or move eastward. You’re 2 away from Moscow with your main force, but you want to be able to take and keep Bryansk or Smolensk if Russia lets you. You’ve had one round to detour a bit to take Novgorod, Ukraine, kill some Russian stragglers, or whatever else.
G4 tanks/mechs eastward to Eastern Poland, 3 away from moscow.
If your planes were messing around anywhere else, begin to move them into position to hit Russia.
Bomb Moscow.
G6:
Buy planes. Tactical bombers from your Ukraine or Novgorod factories, and anything left goes for heavy bombers in Germany.
G1&G2&G3&G4 converge on Bryansk or Smolensk outside of Russia. Bryansk is clearly the tactically superior position, and is reachable by either the north or south route, but if you had people coming from a fight in Archangel killing fleeing Russians, Smolensk is an option.
G5 planes move east.
All of your planes are hopefully on top of your stack so that they can move back as far westward as they can once you have won, and to protect your stack. This, however, depends on whether or not Russia let you keep Bryansk/Smolensk from last round, or you brought some Italian buddies with you.
Bomb Moscow.
At this point, Britain could have flown in a bunch of planes to save Moscow. America might have even flown in some bombers to roll some 1’s and take hits. Maybe Russia abandons Moscow to head south. Maybe you even have some British pushing up through the caucasus. These are all things you need to consider and watch.
You might be facing a big allied landing in the west. Make sure to block tanks from blitzing around, but otherwise ignore this for now. If Moscow falls, you will almost definitely have all the resources you need to evict them. It is not uncommon to lose everything west of Berlin as you successfully take Moscow.
G7:
Option A:
Hit Russia right the hell now. All units converge, planes fly straight from factories. Glorious, fiery death. At best, you’re looking at an 80% chance to win unless the allies have gifted you with severe mistakes. It could be as low as 5-10% against a very careful Russian player with a bunch of British and American planes sitting there. Somewhere between 5 and 80 percent. Are you feeling ballsy? A fantastic victory, or the beginning of the end, awaits you.
If you get diced on Round 1 or 2 of the battle, consider Option B.
Option B:
Russia might not be able to be killed, but they sure as hell can’t kill you either. Dig in for a long game. Start sending only what you can southward to start getting that sweet, sweet middle east/caucasus/volgograd money. Snake around behind moscow and steal his eastern territories if he lets you. You will quickly outpace the crumbling Russian economy.