Substrate question

Not really. Or rather--there are lots of fish that will move it around, but a bit too aggressively. With CC, you have to clean the substrate, since it can never achieve the conditions beneficial to anaerobic bacteria in a normal depth--the grain size is too large. This means there's no worry about 'turn over', just cleanliness. So, unlike a DSB, you will need to vaccum it, though having detrivores like stars and worms will help quite a bit.