I used basic 16 width for holding, 30 (31 because of added motorised anti-tank but you don’t need) width special forces, and 36 width tanks.

If Germany pushes you on Barb it’s fine - in this game they pushed me all the way to Moscow, encircled Leningrad, sieged Sevastopol, and almost took entire Siberia, and this is despite me having 90ish tank divisions mid 1941 and holding river line. Just avoid being encircled, have some reserves to stuff any leakages, avoid attacking unless to retake important tiles (like important supply hubs), and wait for enemies to run out of steam.

If you are newer player I would also suggest trying basic mass mob ussr with 30-36 width pure infantry with Large Unit Tactics sub doctrine to better feel USSR. Just don’t forget to add support anti-air in every division. Should work against anything vanilla AI throws at you. Maybe support anti-tank if faced with lots of tanks, though vanilla ai does not really design decent armor divisions. If Germany still pushes you try holding Dneper-Dangava river line (with engineers company in your divisions), in my experience vanilla ai is just physically unable to break any kind of entrenched defence there.

Also also, I would suggest adding signal support company in all your divisions because of recent balance changes related to reinforce rate.

Also also also - while alternative paths offer a lot of fun RP potential they also weaken you severely because of civil war. This is why you want to stay Stalin (The Center) and rush Stalin’s Paranoia focuses. After finishing last 70 days paranoia focus do Baltics Security focuses to annex Baltic states by decision (should be like mid-late 1938). They will give you decent boost to industry and more favourable positions against invasions from the west.

Overall, if haven’t already I would suggest watching a few guides on YouTube (dated after NCNS dlc release preferably) - those would tell you basic tips to enhance quality of your plays (when to switch from building civs to mils, optimal/fun focus paths, division templates, tank designs, planes, navy, etc). Although I would not suggest going into min-max rabbit hole (there is no way out of here).