Welcome to the board!
I think it's great that you want to rescue an adult. I rescued the guy in my avatar in June and he's been the best dog. He is mildly dog aggressive, but that comes with the territory of wanting a pit bull. You should be expecting
dog aggression, though not all pit bulls are dog aggressive.
At 2 years, a dog will most likely be at its adult weight, though it could still be filling out a little.
My dog, at 53 lbs, eats about 2- 2 1/2 cups of food a day. I recommend reading as much as you can on food in the health section. And pay close attention to posts made by barbponys, our resident nutrition expert.
You can also use the search feature at the top of the page to look up other questions you may have. Most topics have been covered and the threads usually have lots of useful information.