Step 3

In my opinion, it is best to start designing the turret at this point. I recommend using th old rotor, with it being nudged or XML modded to make it bigger or to remove a possible shot trap.
Turret design varies, heavily. Soviet and Russian tanks, excluding the T-14 have; short (height wise), wide, compact, and circular turrets. Even the T-90 has these turrets, although they are welded.
Western turrets, are boxy, and have an angled front in most cases. The side armor is normally thicker than frontal armor . . . due to the lack of angling.
Most modern turrets lack a mantlet, but, I cannot replicate turrets without them in game.
Older turrets are another story, it is completely different then making modern tanks.

Step 4

Drivers hatch, hatches, and engine compartment. Normally hatches are 1.75 or 1.5 at the base. The top is often 1.25 wide at the top, or are XMLed to be shorter, and are 1.5 all the way through. Airbrakes can also be XMLed to be larger.....and set on AVG-7 to act as hatches.
Driver's hatches also contain veiw ports, or have them mounted somewhere. This is completely up to you on how they are made.
Engines are simple, you can either use wings or just let the engine itself provide the detail.
[Eample:Coming Soonish]