I have kept them off and on through the years and I currently have one around Five inches in length that I got last Aug as a Hatchling, that should tell you a bit about their growth rate at least when Young. bear in mind that it grew this fast, only eating once a week and only feeder fish at that with a pinkie every few months.
-Diet: In the wild they are known to eat mostly Fish, mollusk, and invertebrates like crawfish, with random reports they do eat smaller turtles, baby Gators, and carrion. Mine until recently would only eat live fish and Pinkies, it only now started taking mazuri and beef hearts.
-Setup: Lots of Filtration and lots of plants and wood to climb. ASTs are not known to be strong swimmers and many state to keep them in shallow water, my experience though shows that they perfer deep water with structures they can climb and that they can and wil swim when they need to no issue. I have kept mine in over two ffet of water since day one, and he has never had one issue.
-growth rate: see opening comment.
-Size: Males get huge, Females really get no larger than a large CST does at around 40 pounds
-Tank mate: I would be more worried about other Turtles when the AST is young, they tend to nip at their tails. Personally I have never seen a AST aggressive towards another turtle of similar or large size than it, but I have seen mine takle down and destroy a Catfish 3X its size, so be wary
-Do they make good pet: Depends on your definition, Personally I think they cool looking but boring pets. CST IMO make better display animals because they tend to be more intelligent and personable, and far more active and curio