How much food does an eight week old chicken need to eat - mix of different grains, seeds like oats/flax/peas/corn/wheat/sunflower seeds/nutritional yeast and eggshells - plus table scraps available all day ?
I don't exactly know how to answer that question....I guess it's as much as they want to eat??
But for table scraps...Very little every day. If you do feed them table scraps, only healthy scraps such as fruits and veggies but NO BREAD....Bread had NO nutritional value. Just heard from the vet when we took my hen in who had a prolapsed vent because of a calcium deficiency that you technically should only be feeding your hens layer feed, no scraps. Let's say a hen eats some watermelon. It fills her up, thus making her not wanting to eat any layer feed or very little layer feed which is full of all the stuff she needs to lay an egg. So instead of eating layer feed she eats the watermelon which has no calcium, basically none of the stuff that layer feed has. If she has multiple snacks/scraps a day, of course she'll prefer the snacks so she eats the snacks, it fills her up, so she doesn't eat her feed that she needs to lay good eggs. She could lay softshell eggs, get eggbound, get a prolapse, and multiple other things could also happen.
Trust me, you do not want your hen getting any of those. But yeah, if you have scraps, go ahead and feed a small amount to your flock every day or every other day or so

Just keep in mind what I said
I’ve heard mixed reviews about onions and garlic. What’s the deal?
Onions and garlic aren't bad for chickens, it just makes the hens' eggs taste bad

I would only feed it to them once in a great while if at all.