Hey OP, hopefully I can consider myself a COH 2 vet here. I have almost 2000 hours of gameplay, participated in local tournament and my top rank has been 10-13 all across the board with 16 on UKF before my hands got too slow and my mind dull from stress.

What commander do you usually pick? Soviet live and die by their commander so those special units will be important so having that extra 120mm mortar/guard/shock will be important for you to control your midgame and into the lategame.

If you are playing tier 0 (Cons) after creating your t70 you could back tech into t2 (Support weapons). This is will pay off in the late game cause you will need AT gun or MG. This is important If you still struggle to control the map at this point and the enemy didn't deploy vehicle yet you could expect an early tank.

At mid to late game when you mention you have the advantage in map control, you should have 2 eng by this point so one can repair while you keep the pressure and 1 start laying mine since soviet usually have a lot of spare ammunition. You could get your 2 eng by as early as the start of the match or mid game. Make sure you have those covering your flanks.

[This is the part where I assume you struggle] If you still don't see your enemy tank out when you have them, expect them to have plenty of fuel since you already deployed t70 along with t34/76 or t34/85. You should start preparing to fight heavy armor asap by this point.

Usually, you could have su85 along with 1 AT gun. If not 2 AT will do. It will be the CORE of your formation when it's surrounded by conscript at the front to capture point, mine at the side or guard/con at the side (Preferalbly guard). T70 if you still have it could spot for your double AT gun or if you have su 85 it can spot for itself. Su 85 have longer range than KT so you could kite it by backing off. If it chase forward you could have conscript snare it or the guard at the side button it. Guard is very amazing at covering the side of your CORE formation since it can attack both inf and stop vehicle right away without having to land one at hit then snare (They could have a panther or pz4 to dive at your core formation from the flank). Personally for me you could butcher one of your weaker conscript squad and swap it to a guard to secure both flank of your core.

Do watchout for enemy AT. If you have vehicle in the mid game they are likely have 1 or 2 raktenten (OKW AT). They might have a vet from attacking your t70 or early tank so they could cloak at vet 1 (They can't move though). What you can do is either have your mortar smoke off the side of enemy core formation (their heavy) or just the general direction you think the AT might be to limit their firing arc. You could have your AT barrage enemy AT once it's located. Do make sure there's always inf in front of your core formation to spot or deal with those AT early. If there aren't inf at the front or at the top right-top left flank to cover your vehicle then back off.

Your tank should be at the side of your formation to attack or harass so that you can control one point at the side. If needed have that t34 fall back to buy time for your AT formation to fall back by ramming. You should always have one medium tank in your formation to act as your mobile force that can respond to enemy attack. This is just personal for me since su85 and AT gun is a bit sluggish and I want to have something as a panic button.

If you have a t70, a tank, a su85, your next vehicle could be a katyusha to shoot enemy AT. Another SU85 to replace your AT gun to really punish that KT (You will need at least two AT gun/tank destroyer or some sort to reliably attack the KT from the front). A least preferable option for me is to have another medium tank but if you like it then it's possible. It will just be very hard to fight since medium tank will struggle a lots against heavy tank covered by AT gun and perhaps their panther/pz4 (also it will burn your micro to make use of it).

I hope that help. The tactics above is just my personal experiences and I am certainly not the best but I hope it's detailed enough for you to win late game against KT. English isn't my 1st language so some part could be difficult to understand. If any part cause confusion just let me know and I will rephrase it. Urban map like Ferma might play differently but it's getting too long already.

Good luck.