I too would be worried about the eel eating the other fish. Also, an all glass top will cut down on the gas exchange at the surface of the tank and will heat your water, depending on what type of lights you have, so you may have to reconsider the eel if you start seeing your water get hot or your oxygen being depleted.
The rest of the fish should all be fine together, but clowns can be unpredictably aggressive towards anything. So it also depends on what type of clowns you're planning on -- some are more passive than others.