Aside from the clay issue, you don't really need a lot of silos. You can empty silos from the hopper inside the barn, store the hay in a chest, and refill the silo with harvested hay. Or just buy hay and store it in a chest. If you have autofeeders, a cherry bomb by the trough will open up a space and then you can remove hay from the hopper again to empty the silo. I find two silos is optimum for me, just for the convenience of not having to check them frequently and keep filling them up, but strictly speaking you only need one.