I did all of the above on my current one... I'm not sure if that's a bad idea though... I have a bio-ball Sump with a small protein skimmer, a RDP Refugium, currently side-by-side with my main tank, and then also a canister filter that came with my new tank.
I filled the canister with bio-wheels, carbon, and filter foam. I worry a bit about the carbon as I'm not sure at what point that will suck up enough nitrates that my reef will start to starve.