The more filter medium you can put on such a tank, the better filtration-- BUT the more cleaning for the owner. These filters have to be maintained very clean, compared to what goes on in a freshwater tank...that's why fish-onlies are quite a bit more work than, say, a softie reef, where the corals do a lot of the filtering. Probably a good setup, but do try to make a system that's easy to clean.
Having both forms of filtrations won't have a negative affect on your water quality. What size tank? Like the other person said you might not need a HOB filter. Instead get protein skimmer or hang on back refugium. I have a hang on back filter and put all my rock rubble and carbon in there.
Might as well use it. It will also add circulation. Here is a picture of my set up with rocks and mangroves which aren't doing to well. I see people do modification to aqua clears to make them a refugium. This required no modifications. If I ever add macro algae I just need to add a screen to hold it in. This filter also is adjustable from fast flow to drops comming out. Not sure of the filter brand though. For canisters I have a bunch of aquatop/sun sun which I really like. You can get them on amazon. The larger models have A uv light.