Do you know where i can find any place there are document providing any topology and questions?
Main disadvantage is the IOS you can run. With a 2500, you're going to be limited to running 12.2 vs with a 2800 you can run the latest and greatest code. If all you can afford is the 2500, then go for it. It will still be a great tool for you.
(please rate the post if this helps!)