you may want to get a longer tank or multiple tanks so you can have better biological and mechanical filtration before the "live" part of the refugium.
dont put any fish inside it, but you could have some java fern, java moss, or other low-light plants inside; you will still need to get a light. put some inverts in there like ghost shrimp; just feed them every day or so and they can help keep the refugium clean. they will probably breed alot if you have enough of them, and that will be a great live food source for your fish in the main tank.