If you're not comfortable using PVC -- worried about cutting to size, fittings, and glueing, you can always use flexible tubing to plumb the drain from the overflow box and the return line from the sump to the display. There's also a flexible drain hose that's commercially made that looks like vacuum cleaner hose, with a fitting on each end designed to slide over common overflow output fitting sizes.
What kind of HOB skimmer is it? There's certainly tanks that utilize HOB skimmers that are sucessful. Installing an overflow and a sump itself doesn't automatically help the tank be any healthier. You can have a very healthy and sucessful tank without a sump.