[Pescador]

Hey
How big is your tank? If you have 1 to 1 1/2 lbs. of live rock per gallon you don't need the biowheel or any other media for biological filtration.
You could probably keep one of the filter trays for mechanical filtration if you change it frequently.
If you can remove the wheel and trays would that would free up some space in the sump? If it does see what the biggest skimmer footprint is that you could fit in there.
For nitrate levels I think most people with corals try to keep the levels under 10 ppm. Fish only tanks can be much higher.
I have no experience with sea horses but I don't think many people keep them in a reef because of the high water flow needed and I don't know about their tolerance for nitrate.