Tanks, very much like the shock cavalry of past wars, have the fatal flaw in that they cannot tactically defend. The advantage tanks have is that they are all terrain armoured artillery pieces, defending then invalidates one of the core features of what makes a tank good. More importantly defensively speaking tanks are absurdly vulnerable, since the stationary tanks are easily bypassed, or are easy enough to bring fire support to nullify them. So smart tank usage is not the defend with them, seeing as defending throws away all of their advantages and makes them very expensive inefficient pill boxes.
When faced with defensive operations, again like shock cavalry, counter attack the enemy. (This can lead to the confusing scenario when you have tanks fighting tanks - who is really attacking who?) That is the only truly defensive tactic a tank is good for, attacking the enemies attack. Otherwise you would be better served with the same logistical weight of at guns + artillery, or even just grunt infantry.
So if you create a solo tank division be prepared to micro it a lot as it's completely specialized at offensive operations now. While potentially able to be devastating when used properly this kind of division leaves no tactical room for commanders, and forces the rest of your army to protect them from counter attacks. Its probably more strategically efficient to keep the tanks as a last resort counter attack weapon than an actual offensive army if you have no ability to give mobile infantry support for them. At least in the counter attack roll they will always be used properly.
