cmor, yes, if you have an ATO that tops off regularly, then you won't see the bubbles.
nick- you'll need an auto top off as well.
you don't have to worry about your drain clogging up. i've never seen that happen.
your sump will hold whatever drains from the display if you have the return line just under the water surface, or have a hole drilled in it just under the water surface in the display. otherwise, it will drain the DT down until the return line starts sucking air and breaks siphon. this might be 4 inches of water or more depending on how you have it set up.