What size are you planning to make? I just made one out of a 10gal for a55gal which is pretty small in general. Because it's tall, surface area is smaller so I'm getting away with it as far as back flow could go.
My honest opinion (from reading for a few months now) on anything 20gal or smaller is that the sock filter setup (unless above the sump somehow and dripping in) is a waste of space. I wanted to do the same thing but you can do just as good mechanical filtration on top of your bio media and get more media in the actual tank with some better planning.
It's just my opinion and I'm not an expert as you'll see in my build thread... I'm still modifying it. I'm cutting my refugium wall down about another inch and slotting it to give myself better piece of mind in the event of a power outage and some back flow.