the only thing i would really add is this. if you can't make the vehicles make sense and positively and seamlessly add to the gameplay then just stick to the three armors only.
T1 vehicles were largely irrelevant.
T2 vehicles were retarded and OP.
T:V again, retarded vehicles.
nobody has had vehicles that were both useful and balanced w/o having to have a hard counter like heat seaking retardo rockets.
I would say that the Tank in T2 came closest to usable and balanced.