Fermenting and Amprolium: I have no idea how fermenting affects Amprolium. You can ferment medicated feed. There are 2 schools of thought on Amprolium: Cocci is everywhere, in all soils, and a natural flora in a chicken's gut. Amprolium is a Thiamine blocker. Thiamine is required for the cocci to reproduce. So, the medicated feed campers, figure that the medicated feed will limit the load of cocci in the gut to give the chick time to build a healthy flora to outnumber any cocci. Common mistake is taking them off medicated when they move out into wet soil conditions. Then there is the other camp, of which I am a strong proponent: Cocci is natural. Chicks have the highest natural immunity in the first 2 weeks after hatch. During that time, I want to expose MY chicks to the specific cocci strains that are in MY soil. At the same time, I do everything in my power to boost their immunity: give them a plug of soil/sod from my yard that will give them a good dose of bacteria and fungi to jump start their gut flora. Give them fermented feed, again, to do the same. Lots of probiotics in FF, and they do absorb more nutrient, and their gut villi grow longer, allowing them to absorb nutrient from all sources with more ease. Also, by keeping your flock off bare fecal loaded impacted soil that is often seen in many closed chicken runs, you will decrease ALL pathogen exposure. (deep litter here, as soon as the soil becomes visible in the run) My chicks have NEVER had medicated feed. I've never had issues with cocci. I can't imagine ever needing to give medicated feed. Last spring, I had a poor hatch of shipped eggs that was compounded with some incubation problems. Those chicks were not as thrifty. But, just as soon as I got them on 100% FF, they perked up, and their stools improved greatly.
FF protein math: You can research some studies. Or you can simply try it and enjoy the benefit. My chicks have always laid at least 2 weeks earlier than the chicks of my friends. (Same breed, same source, same age, same feed store options. In multiple instances the chicks of my friends have come from MY incubator!)) Only difference is FF.
They will eat less feed because they absorb more nutrient from the feed that they do eat.