under the general premesis that when the syphon breaks it is because of a power outage, thus the pump would stop and the auto topoff would also stop. so no filling, when the power comes back on , pump starts and if the drain from the main tank is a u shaped type, you would get flooding, a internal drain starts and no flooding, a glass top on the sump area is not a good idea, you need that oxygen exchange. and the mh
light on one side wouldn't hurt, but, it might be better to put it in the middle and allow the spread of the light ( about 3 feet per mh
) to light the whole tank.