Levels - The maximum level in DI for the time being is 50. If time goes on and it needs to be raised, it will. But until then, it's 50.
Equipment - You can carry the equipment you're wearing, and an extra set of equipment.
Example: Lets say you're a Knight. You're wearing all your armor and stuff, then if you like you can carry: An extra set of gloves, an extra set of boots, an extra shield, and an extra sword. (Or if you use two swords, you can carry two extra swords, instead of a sword and a shield).
Items - You can carry all the standard items you could ever want or need.