Questions on how I should upgrade my infantry

[Imp]

Mobhack is right if make mixed platoons standardise them.
O unit is good as a support unit so takes less fire & has more chance to rally platoon.
Then decide mix of infantry to tank killer.
Can be a good idea to keep third platoon as a dedicated unit like tank killers.
If used SMGs would do entire platoon for use in woods & urban enviroment, not that usefull in a mixed platoon, suppose he would be point man.