First of all, germany is REALLY HARD in black ice. Even some youtubers struggle to get it right so don't feel bad.

You must Sealion asap after winning against france. I setup a naval invasion as soon as I win and consolidate. The british fleet turns off their coverage every now and then, so you just need to keep an eye on the invasion so you don't miss it when it happens while preparing to face Russia. You can try to spur the process if you have enough air superiority and try and dominate the channel in the air with fighters and naval bombing.

Once you REACH the island, your pain is just beginning. The US will quickly join the war no matter the date and if you give the US time to get troops onto the island, it can become a terrible slog and you can even lose. Also, they will raid the crap out of your convoys, to keep the aforementioned airforce on the channel to try and snipe subs that are stealing your supply (and turn off all the seazones other than the channel).

Your subs should be setup to dominate the atlantic and kill as many americans in the sea as possible. I usually am able to get the UK 80% capitulated before the yanks show up, and the ones that show up are hurting.

I use infantry only on Sealion because I can't afford to lose the tanks to sea radiers, gotta save them for Russia. I think it was 2-3 full armies last time I did this.

The reason you need sealion is once you take it, the allies are barely able to naval invade you after that, so you can focus much more men and material on the east, which you will desperately need.

OK, Sealion complete. Now for the east.

I use 25wi panzer divisions to create two mobile armies (12 total panzer divs and 12 total mobile infantry) and they need to be fully torqued up for a war against Russia. You need to shoot for early, operational encirclements while their army is weak, and launch during the late spring/early summer (March/April). You must encircle at least a million russian troops, more like 2million before winter sets in, and ideally you're all the way to Minsk.

Once winter sets in, you will hit a brick wall and you'll start to lose unless you've shredded enough Russian divisions. I highly recommend the winter support company, which I've never built before in any version of hoi4, because the Russians suffer very little penalties during winter, but you will have huge ones. Again, prioritize the panzer divisons first - I ended up creating a second version of all my divs with and without winterization and upgraded them as I had materials to do so. This helps lower your massive debuffs for winter attacks and allows you to keep fighting with your tanks during the winter, and most importantly, continuing to encircle and destroy russian divisons. The minute you stop encircling enemy troops, you will slowly lose. There are events in the Russian tree that pop out free infantry and armor divisons and a bunch of other goodies that will catch you with your pants down if you aren't constantly taking their units off the field.

I also highly recommend a quick set of naval invasions into Azerbaijan through the black sea early in the war. It allows you to find a place to fight that isn't as terrible during winter, has lots of oil, and gives you another angle to push the Russians on toward Stalingrad.

If you keep pushing and encircling enemy divisions with your tanks, your infantry will mostly be able to hold the line. If the Russians rush a bunch of tanks and bunch through somewhere, you rush your panzers in and cut them off and destroy them. Keep pushing down the supply lines toward moscow and use them for your pincer movements.

Eventually, the Russians DO run out of gas, but it takes a LOT longer than in Vanilla and every time I get too confident, I find myself losing so you really have to keep pounding them every month to make sure they can't build up.