You will find that you cannot maintain 4 manufactures of basic goods while adding seed and sentient goods production.
Yourself and
@QnAthena may come to this conclusion. For comparison, I kept 6 x planks, 5 x scrolls, and 5 x dust. It is a constant battle to maintain seeds and unurium, but that isn't the fault of my manufactories.
I have 1 x marble, 2 x silk, and 2 x gems for my sentient goods. These are just right for what I need. I could sell one each of the silk and gems, since they are there for when I need a boost to depleted sentient goods, are are usually just producing standard goods at a low rate.
Also, 1 x steel and 1 x crystal keep my ascended goods at the right level, most of the time. Unurium costs right now are the limiting factor.
Having goods surplus allows me to take FS trades quickly, and to offer an occasional 'special deal' where appropriate.
There are many ways to play the game