3) A cell signal is not required to collect data. So no data would be lost in areas of poor coverage. It will just upload the next time a connection is regained. However, the ability to share coverage between combines live while harvesting does require an internet connection to work properly.
4) The Field Health images automatically adjust to expose as much variability as possible on each field. So the difference between 60," 30", or 15" rows shouldn't matter. The areas in gold/yellow on this map do not currently have Field Health imagery: https://cl.ly/o7mj