Which ever you choose, it will need to be maintained, and if you know it's limitations it will serve you well. I personally use a shallow layer of sand in my main tank and a 4" DSB
in my fuge, if I experiece any problems associated with a DSB
going south, I can take it off line fairly easy.
As for your fuge, I would recommend no less than 10% of your tank volume and preferably larger.