The whole turret idea remind me of Archimedean Dynasty.
You could order turrests to shoot down incoming torpedos, attack hostiles or attack your target, or fire in sync with your main gun.
Anti-missile system anyone?

The whole concept is becoming more and more Mechwarriorish:D ...not that I would mind.
Adding a certain number of slots to a fighter - for missiles, lasers, and ballistic guns, plus omni slots that would fit anything players would have a huge variety of combinations at their hands.
To make it FS consistent, the onboard targeting computer wouldn't handle infinite number of weapon systems, so weapons have to be chained together into groups and each group could contain only similar weapons.
Ingame instead of the weapon names you'd be given GROUP 1, GROUP 2 - and another console to tell what each group holds.
We could have more than two groups but then more control would have to be given to the pilot - a very Mechwarriorish weaponcontrol.
Adding external and internal slots and a slot requirement for weapons could fit nicely with all the systems or tertiary weapons.
Each weapon could have a damage treshold of its own, so outside systems - like turrets - could be blown.