Can say one suggestion, instead of Katyusa it would be cool to take M30 122mm and make it mobile . Then infantry can push it around for point blank arty support like in real life. I mean, there is already lot of tanks but thats just instead of Katyusa if you plan to put it.
Or it would be nice for Germans, as their artilery in city did last stand, to place one movable LeFh105 . That would be used to support defense as they dont have much tanks. Disable that look-from-air that arty usualy has so it can just fire at point blank direct fire. And make it from third sector avaible. Take code from Pak or some other movable gun. And as its slow, germans will need to place it clever and retreat when too close to enemy.
Just something I taught as I looked some videos of battle of berlin.