Ive been making instant pot stock for quite some time .
not sure if iPots are available ubiquitous in Japan. its an electric digital pressure cooker.
IVe made turkey stock from raw and roasted carcass. I re-use that stock several times
rather than starting w water each time , as its a way to concentrate the final stock w/o having
to reduce the water initially . I use no seasonings with this method , as they might over concentrate
especially if using salt.
Ive tasted no off tastes from repeatedly doing this . I rapidly cool the stock, then regrigerate ,
then freeze in vacuum sealed bags.
from this experience , and a recent one here :
https://forums.egullet.org/topic/167159-stock-instant-potd/#comment-2437466
I see no advantage in doing the feet separately , as long as you are using enough water
and time , with the whole combination
are you using a traditional stove top PC ? do you have an iPot ?
BTW , Ive found seasoning the stock later is more flexible than seasoning initially .
and the resulting stock's flavor can vary w your expected use each time.
good luck .
please consider posting your experiences .
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and pictures are always appreciated , including some of your steps
if you have the time.
P.S.: if you plan to get the most flavor out of your chicken into the stock
chop the chicken into smaller pieces , thus increasing the surface area of chicken :: water.
there might be little flavor left in the chicken , but that's because the flavor is now in the
stock.