Additional note on this point.
4. If you skip a level, it simply unlocks the next level. You do get a popup asking if you want to start the next level, but always decline that. If you accept it, you auto-abort your current level.
If you're planning on using a Skip Level but also plan on finishing the level you're playing and not aborting the level, then
DO NOT use a Skip Level. Using the Skip Level is wasted, b/c it will unlock the next level which would also automatically unlock simply by clearing the level you're playing.
Always use Skip Levels AFTER finishing or when aborting a level. If you finish the level already & closed it, you will need to start a new level to be able to bring up the Power tab to be able to activate the Skip Level, and then go ahead and abort the level.
By FINISHING the level first, you will actually unlock an additional level.