fenrizwolf, I felt the same way about not trusting an HOB overflow. I did the same thing you did; I have an HOB skimmer. Mine is a CPR Bak-Pak 2R. I got it on ebay brand new for less than $90. You can find them from a seller called amekaaquatics; they're units that had damage to the skimmer bodies and were factory-repaired. Mine works fine; however, I will warn you that you need to adjust the valve on the front of the Rio powerhead that's included in order to actually have the skimmer produce skimmate. I learned this the hard way, as mine didn't produce any skimmate for the first few weeks and my nitrates built up. You'll also want to look into getting the Pre-skimmer for the Bak-Pak, as it reduces the protein slick on the surface of the tank. For sand, I used the CaribSea Arag-alive live sand, and I have no complaints about it.
EDIT: Just noticed you already chose a skimmer. Yes, you do need the saltwater test kits; if you have any API kits for freshwater tanks, most of those work for saltwater too. You can get the full set of saltwater test kits for $25 - $30 and they work fine for me.