I. To see altitudes (either relative or absolute) for traffic, you need to be zoomed in to a certain level. To choose between relative and absolute altitudes, tap Menu > Setup > Alerts and Warnings > Traffic Alerts, and then either check or uncheck "Show Relative Altitudes".
II. Your flight plan persists until you change it or clear it. If you want to delete it, tap Flight Plan, then the "Clear" button in the upper-right corner.