An important feature to remember is that the level editor is 'live'.
Any testing you want to do in the editor you will need to rewind afterwards, and any major testing should occur in Play mode.
Switching between PLAY and CREATE can be done in the pause menu when you are in a level on your moon, you dont need to exit the level.
Also, "RECENT LEVELS" does not show recently uploaded levels, it shows levels that you have recently played. not nearly as useful.