[Andrés]

Building one of this things takes many decades and many resources. Only being able to do it is a display of power.
Minimun mov is 1.
Yes I'd given those large ships defense penalties of that order. This does not change range of weapons, as soon as the enemy is in range it will have 100% chance to hit.
I know that any kind of ECM is usless, the target is so large it's impossible to miss, but that's not a problem since it can also absorve a lot of damage, even if you can skip its shields and/or armor, you'll need a lot of firepower to make any significant damage.
Damage a ship of this size depends more on its multiplex tracking than on its weapons, with its massive firepower it will be able to destroy as many smaller ships as it can track each combat turn.