I strongly recommend armoring magazines.
Do you expect being attacked soon?
Otherwise, I would wait a few months, research some tracking speed and turret, and then build a PDC, because, this ain't stopping anyone.
Well, atleast not anymore in 2 years.
Keep in mind PDCs can always reload from Planetary stockpiles, so you don't need that big magazines.
Against Missiles, you can also get a tracking speed bonus, though you have to research that aswell.