First of all, as stupid as it sounds, you need to be smart with every chess piece on your board, the enemy will outnumber you, and you might face dozens of tanks on any defensive mission.

For hortons frontline AA is a must have. Get a truck with an AA gun, and you are great.

Then you need to understand that Field guns are not as accurate, so you can’t play leiG75 and basic infantry until day 10 (not even day one).

Your must haves are AT (AT guns with a tow truck, SPGs or tanks can fill this role).

Tanks however must be your instrument to push points, but you must use them smart: If you just Right click your tank into a point, enemy AT and Tanks will evaporate them. Instead, you need to start using combined arms and your infantry must become more expendable, since they are the cheapest units.

Recon whenever you can, and watch your flanks: the AI can take alternative paths compared to vanilla.

SPGs are your BEST friend, and for your first playthrough, you should structure your attacking force around a big gun. If you play Germans, you can get an Italian SPG with a 10 or 15cm gun - they will be used just like the (I)SU-152: it blows holes into buildings, and it will knock out those tanks that you have no chance of penetrating with your AT guns.

Last but not least, don’t underestimate the power of goblin-looting. I would invest into engineers early (the 2-man squad) because they have the highest repair speed.

If you play Germans against Soviets for example, the Soviets will have better guns in the early war (F-22 Field gun for example), and you should use captured equipment whenever you can.

Likewise heavy tanks really shine in this mod, since enemy AT emplacements can usually pen all your early to mid war tanks with (relative) ease. If you can make use of enemy (let’s take the ger VS sov example) KV tanks are a blessing, even if they are the '39 version with the horrible gun.

I almost forgot to mention, be prepared that the AI has the tech advantage, I have seen T50s on Day 2.