First, you need to decide if it would be a wild Mandarin, or an ORA captive bred one. Each have their own issues that make them more difficult to keep than other fish.
It is my understanding that the ORA ones eat pellets, but they are not good at competing with the other fish for the pellet. This means you need to figure out a way to make sure they get some of the food at each feeding.
As for the wild ones, they need a large and thriving pod population. If you have a large mature tank that has an established pod population, you will likely be fine. If you have a small or new tank, you will go broke constantly buying pods for them.