Actually, there's more to it. The bark you have him on right now is not the best for him, it tends to mold with high humidity, and if he swallows it, it will cause impaction, which can kill him. At this young stage, it's probably best to keep him on paper towels or repti-carpet.
The care sheet goes into more detail, but here's the basics on a cage he'll need as his grows. Water dragons need height rather than length, so you will need to get him a cage that is taller that it is wide or long, with a lot of things to climb on.
His water source can be a blocked off section of the tank or a bowl, but it must be big enough that he can get his whole body into it, to soak. Water dragons love to swim, so it's a great idea to give him some "bath time" in a bath tub a couple of times a week.
Also, please read the caresheet and check the temperature and humidity requirements. These need to be met to keep him happy and healthy.
I realize that you are selling him, but it would be a good idea to be familiar with these things so that you can find a person willing and able to take care of him properly.
I hope everything goes well with him.
