Specific questions follow, although I am interested in any worthwhile information. Over the years, I have experienced a few walk-home failures. I enjoy running and usually just run on to my destination, with or without wheels. I may resurrect my old road bike for when I am in a hurry, but this pedal shoe combination is primarily for bents. Undoubtedly more questions to follow.
Float is good.
You want float. The first generation of clipless pedals locked your foot into a fixed position relative to the pedal. The amount of float is indicated in degrees, and depending on the pedal you choose, can be as little as 4 deg or as much as 35 deg. Some pedals offer variable release tension. This is a separate feature.