That formula might work for social herbivores in a productive environment but probably not for carnivores, even social ones. A mountain lion can need 100+ sq miles and they only weigh 80 lbs. Really lush and productive flora could support more prey animals but there's no info on where that might occur, certainly not everywhere.
That isn't always true. I gypsied for 15 years as a wild youth. When money was short, I made ends meet by fasting. It's not a big deal if you control stuffing yourself (just follow the rules of fasting). The result has been that no food is always a temporary condition because you already been there way lots. Pro tip: don't break a fast w/ junk food :)
Won't the old beak Keratin still grow and deform the new plastic beak, or even push it loose eventually? Anchors will probably hold for awhile but Keratin is like fingernails and it'll keep growing underneath. Depending on the pressure it exerts, it may become impacted like wisdom teeth.