I did the hole in the water line trick but it caused a lot of salt creep, so I was glad when it clogged.
Not if you start with the sump full when the power is off. The level will go down from there (into the main tank) when you turn the power on, and will return to that level in the sump when the power goes off. It is so hard to explain things when you know what you mean and others have no clue. With a couple of little pictures I could make it perfectly clear.
I have a spare wet/dry filter a little larger than the one in the picture. Too big for my cabinet. It was just being used as a refugium, so I have no media for it.