" Question is, how much chicken do you need to make a decent chicken stock? "
The answer, as always, is 'it depends'
. It depends on how flavoursome you want your stock to be, how much you expect to get from one carcase, if you are happy for most of the flavour to come from the added veg or you want it to taste of chicken.....and so on.
Unless you have already cracked the bones and sucked out the marrow, there will be some of that to give flavour to your stock, but otherwise bare bones really aren't going to contribute much.
Apparently during the Second World War, cookery advice was given out over the radio, as with the 'dig for victory' info. My MiL picked up the tip of making the stock
before she roasted the chicken, and she carried on doing that forever. My goodness it was disgusting
The 'soup' itself was like water with a few rice grains added, and the bird after a brief visit to the oven was rubbery, slimy and tasteless. Even now my OH doesn't list roast chicken amongst his favourite meals and won't eat chicken soup at all.
I think you can take economy too far. I much prefer using a couple of rashers of fried bacon as the basis for my soups