I like to have 999 enhancers on each factory (for a total of 1000 item production) and then if I need less, just add less material in. But I never automated my factories very heavily except for temporary cross-linking for specific orders (eg. gray hull and black paint running in two factories, and a third factory drawing from both of those to make black hull), because I was generally worried about accidental overruns, like using up all my fertikeen on 5 million fert motherboards or something while I'd stepped out for a bit.