i would start with balance and bugs to get the former as good as possible, short of an overhaul, and get rid of the later. then i would overhaul the things that needed it. you can make the game ok with just balance/bugs but an overhaul is really needed for soviet/OKW, OKH teching, and USF very early game.
OKW is severely punished for choosing a vehicle. if they have to build pumas/JPIVs you will never see anything heavier in an even game. assuming they're not carried by infantry of course. the other issue is that they have a hard time replacing losses.
yes, but it should be buffed. making it cost 100 fuel and be as effective as a zis gun (along with being swapped with t-70) would be an excellent move.