STL Check is a modifier you can place over the top of your lowpoly for instance, to check if you have left open edges, multiple edges, double faces. It also highlights where these areas are and I use it as a last step before unwrapping and then before export.
This is my biggest problem with high poly modeling but your words are very good to hear and make me want to step down from thinking too big and work from the ground up so to speak. My models do nothing BUT pinch hah. It seems there aren't massive resources available to learn this kinda stuff. I can't wait until Gears 2…