Roast the bones.

I wouldn’t use cruciform veggies in stock - they’re already a gas engine for humans, who knows what they do in stock (my guess is make it bitter).

Start simple - my chicken stock is little more than just a chicken carcass in water. If I have some onions or carrots, I’ll throw that in, maybe a bay leaf. It comes out nice and brownish, concentrated enough that I usually have to thin it with water (I use a pressure cooker or instant pot).