And to continue on with what TCLynx was advising optimally you will have 12" of media in your bed, with the top 1" being kept dry. But, again, for a smaller starter system like yours you could get away with less depth. Best media is a product called Hydroton - light-weight, easy on the hands, holds air and water well. It is pricey, though, and pea gravel works as well.
And, yes, I recommend you start with media based, and consider moving to raft if you decide to go commercial.
Please post a photo when you get setup!