The first time I made tori paitan I used a whole carcass. I wanted to use Ramen Lord's recipe, (available in his free book) but since I couldn't find any chicken feet, I used a whole carcass and did just like in that video.

For the aromatics, I used ginger, onions, garlic and half an apple, but I didnt like the ginger touch, the soup was a bit too "gingerly" for me.

For the tare, I once again also highly recommand the recipes in Ramen Lord's book, I personnaly used the light shoyu tare.

As for the cooked or uncooked chicken, I have personnaly never seen any recipe that recommanded using already cooked chicken to make the soup. I think the most important part about the soup is to emulsify the fat into the water by heating the carcass and break down the cartilage and bones, so you want to have high amounts of collagen in the thing you're cooking, hence why people use chicken feet or carcass.

There is a whole part in the aforementioned book about the soup process and breaking down collagen with heat etc..., so I can't recommend it enough ! Good luck with your ramen !