I can't see why you couldn't get more of something, but honestly, I was always SO FULL I could hardly cram down the 5 desserts I wanted to try. Seriously, going hungry is not a problem there. And if you are still hungry after dinner at the ala carte restaurants, you could always hit up the buffet and/or the grill. You will not be lacking in delicious food to try. And the more variety the better in my book! As for crab legs, can't say I've ever seen them there, but I'm not a big crab person, so it's possible I just missed them.
The soups are fantastic. I recall one dinner when I told the server how much I enjoyed the soup. "Would you like another?" So I had another bowl of soup. She offered a third, but I had my fill. You can eat as much as you want. I don't know about the crab legs (availability).