I know this might not be what you are looking for, but after spending many years working on „my duck“, I now do legs & breasts, both sous vide. Convenient to prep, very reliable in taste & consistency and easily scalable. Pretty good sauce based on reduced bag juices & whatever tickles your fancy in an instant.
In that case one leg (350-400 g) per adult (and per super hungry 7 yo, too), or about 2/3 of a 400g breast (all weights precook).
Edit to add: you can of course trim your whole bird(s) down, and get a free gallon of duck stock plus some duck carnitas out of your carcass ...