get gun first, then turret and then hull

the hull keep using the bagelpanzer hull, the TOW Humvee is just to allow you to do more daily missions and eventually unlock the LOSAT Humvee if you are interested in it (its not very good)

the turret has a lower reload multiplier than the previous Sheridan turret but you get a roof 12.7mm and the armour sometimes works

the gun has good penetration and very high velocity, but requires good aim for the APDS shell (the shell I recommend using)

edit: I KNOW YOU CANT PUT A TURRET ON THE TOW HUMVEE BUT YOU HAVE TO BUY SOMETHING