I would take out the bio balls, as they collect stuff that will add to higher nitrates unless cleaned regularly. I would add some live rock in it's place.
The coral inserts will likely end up covered in algae and look bad in very short time. I'd skip that idea and just go with rock.
Overall, your live rock and live sand will host beneficial bacteria that provide biological filtration. The skimmer should get most of the "solids". Make sure your flow is enough to keep stuff off the sand, so it can eventually get caught by the skimmer. That takes a bit of tweaking usually.
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