On average it would be 1 lb. for every 2 qts. water to get a nice stock. I like to add a few extra lbs. so that it's extremely gelatinous. I make more of a condensed version which means I can add more water to the recipe I'm using it for. Also, having it condensed means I can use a tablespoon or two in while I'm sauteeing veggies or something like that. Overall the condensed version just goes farther and takes up less room in the freezer. I use a 20 qt. stock pot which is a lot.
There's so many different ways to prep the feet for stock, some people skin them first, trim the toenails etc. I like to make it as easy as possible. I do wash them thoroughly but that's about it. Some folks like to parboil them to reduce foam. Keep in mind if you do this you are also reducing nutrients. You will need to skim the foam, but I've never found that to be a problem. It only takes a few minutes to do.
If you are so inclined search the net for chicken feet bone broth and read how other people do it and then find what you are most comfortable with, but whichever way you decide you are not going to regret it.
Here's what I toss in to the pot:
a couple of bay leaves
some fresh thyme if I have it
and after skimming I'll toss in some whole black peppercorns. They get caught up in the foam if you add them at the beginning.
Also, as with any stock, never hard boil it, only gently simmer and never stir a stock. You will get a much cleaner stock.
After I'm done making the stock I pull out all the veg and add more water and fresh veg to make a weaker stock. This gets used when I make rice or boil potatoes. That sort of thing. Let the stock chill overnight and then remove the fat cap. I save my fat cap and freeze it. I use the frozen fat when I make chicken sausages. Hope this helps!!