Countering maxim spam is hard, but it can be done, i think that the first 5 min are very important. The idea is to start capping with one unit and hold another in support, hidden, and when you engage a maxim try to flank it with the one in reserve, hear a kubel is gj, and try not to blob, try to keep a space equal to the maxim arc between the units when trying to advance
With both grenadiers and panzergrenadiers is better to keep a distance from your enemy, because both US and Soviets are pretty useless at long range. I used 3-4 squads of Pgrens very efective againts the Soviets on Moscow just by the fact that i keep a distance from the shock troops.
T70 is good in killing Luchs tanks but you have to remember that it has to fight it with its frontal armour, rear armour of t70 is so weak it can be quite easily killed even by 222.
USF are good early game (cause of the Riflemen) and i like to get an early HMG just to stop there advance. Then i go for 3 gren squads to help me with capping, and after them a mortar. Try to always harass the fuel point.
Try a combination of Is-2 supported by T34-85s, you have good anti-infantry and anti-tank. Also if you hold fuel points, that doesn't mean that your opponents don't receive any fuel (supply chash, trading mun for fuel)
The Stug E is much slower and does not have a turret like the t70, also from the tech you have done to get the t70 you have other options, but if you don't tech and go for a Stug E you don't have that options at all.