GG I guess, AI
So my first thought was that I really wanted to try to hold cities. I had noticed that rifle infantry get REALLY GOOD NUMBERS in cities compared to clear, and I wanted to use that since my rifle divisions were kinda weak (i.e., all 1/1 to start). My basic rules were, "stay adjacent to the rest of your corps, put infantry on the furthest heavy woods/marsh/city that they can reach." And I just ran east for a turn or two, before deciding to try and hold river lines. I also just kind of dumped reserves in a panic wherever I could starting the literal first turn.
Cavalry went to the south where I would eventually learn to use them to just sit next to the enemy to deny them CPP: they would either have to move around ZoC 1/1 cavalry units (silly) or spend half their existing CPP and a couple extra movement attacking. Then I would run the cavalry back to a point where I would use it to start building fortifications. At first I was refitting them, then I started merging them or disbanding them, but eventually I settled on sending them back to the reserve. I don't really know how expensive this was in terms of manpower, but I would have guessed it wouldn't be too bad: horses are pretty good at running away. (It's their raison d'être, you might even say.) If I could, I would slip my horses through the lines and try to capture depots / make officers move (displacement = retreat losses = HAHA SUCKS TO LOSE TRUCKS).
I set up fortresses at Smolensk, Odessa, and Kiev. Odessa had 8 rifle divisions attached to a rifle corps because I made a mistake. Smolensk had I think 6 and an army, and Kiev had 9 with an army. In both cases I tried to use nearby defensible terrain (marshes and heavy woods!) to create linked chains that would make it difficult for the axis to surround the cities. Odessa I just left to its fate, trusting that the 8 rifle divisions could hold with their fortress CV of like 350.
Smolensk fell because I used the marshes to create a corridor and then realized I couldn't keep resupplying Smolensk, which was an anchor point for my line (I tried to anchor my lines in cities since I could put good depots there), when they stepped into the corridor I had left open forgetting that the corridor was the rail line. Whoops.
Kiev fell mostly because the AI punted away panzer group 1. This one I'll show with pictures, because it's beautiful.
T6:

T:7

T:8

We captured 500 panzers. After that, I dunno, it felt like it was probably game? There were a few times I had to react to some big infantry threats elsewhere, I had a few failed pockets, and I had an absolutely disastrous defense of Leningrad which was isolated before December. But I was able to move my armor to the north and having the extra two armies was enough to make it pretty easy to hold everywhere that wasn't Leningrad.
I did see the AI start making maneuvers on the last couple of turns which are on the current patch, so I'm excited to see if that's an honest-to-god AI change.
Some thoughts:
1- it's really hard to tell how much the weather is affecting anything in game. Like it's not clear to me how different snow levels 1, 4, 7, and 9 are except that one of them is "heavy snow" and one of them is "light snow" and there's a "snow" and the more snow the worse. Something something armor breaking down? Literally all I could find in the manual is one sentence about there being a percentage chance to lose tanks? It wasn't clear if that only applied to the Axis during that one winter or...
2- Support Units are driving me crazy. The auto support doesn't make sense and I also am not sure how to make it go away? But some of my units don't have it. I also have no idea what's happening to the support units I bring in from reserve, except that at least some of them are appearing at fronts and STAVKA.
3- The Air War is similarly driving me nuts. I had hoped that I would be able to tell my planes to stop flying during the night but that didn't stick it just reset everything the next turn. So instead I just turned off the ground support button during bad weather.
4- Am I supposed to leave units in my national reserve? I was basically just dumping everything with ToE>75% onto the map. I also dumped all the cavalry all the time. But yeah if you were ToE 75%+ (I think I started calling in 60+ rifle divisions somewhere at one point because I had shoved everyone everywhere), you were on the map somewhere, probably digging forts.
5- Swamps are a gift from god. Heavy woods are deeply magical places that deserve to be protected.
6- I love separate rifle brigades enough that I am sincerely planning to have my infantry armies being 9 divisions 3 brigades. They're like a little salt and pepper and they let you secure so much flank.
7- I love cavalry. I love sprinting behind enemy lines with them and taking back cities (the AI let me nab Smolensk, Kiev, and Riga for a cool +18 time bonus in summer '41 lol). I have the sincerest hope that my destruction of supply depots affects the enemy, even if it's just making them pull from further. And their ability to SCREEN! So many times I would just, especially in the winter, stick a cavalry unit right next to the enemy's doomstack of 3 panzer divisions. They'd smack it, it'd run 10 hexes away and be depleted, and there goes their CPP and ability to move this turn.
Anyways, fun game! Victory was too easy. Next step is to learn more about the air game... probably by doing StB because I don't have too much interest in redoing 1941 so soon.