Re: How much food for a big kitty?
That flappy thing on her belly (which would indicate a lot of weight lost on a human), is very common among adult fixed cats. It really has nothing to do with obesity or lost weight, it's just a flappy thing. Both of my boys have them, and one could actually stand to gain a small amount. A vet can tell you if the cat is overweight, but if you look on line (sorry, can't search now, on my cell browsing) see if you can find a body condition chart for cats. - think the purina site has one.
It will show you a "birds eye" view of the cat, and a side shot. Ideally, from the top you should be able to see a waist on your cat. You should be able to feel the ribs, but not see them. You can check your new family member against thye chart to get a better idea of where your cat "weighs in" (HA! Pardon the pun!)