Unless the mechanics have been changed, and unless autobombs are cheaper than fighters, then I am pretty sure that 10-20 engineers are fine for producing from one space dock, although more spacedocks would be a bit cheaper IIRC, and take up less of the important engineer cap.
After all, Unless it was changed or I am remembering incorrectly, then the max rate of production from one space docks is 5 ships a second, and hence you would need a LOT of engineers to hit that cap for anything more expensive than fighters.
