Have you drilled holes into the drum itself for plumbing yet? If so what did you use to seal? Just a bulk head fitting? Its bloody impressive. Being that big and so much media im guessing you could run the next "something bigger" off the exact some design and be more functional then a sump.
How will you clean the bottom of the drum of crud? I mean im sure a big siphon will get most of it and the wool will catch most of it.
If i ever get a large tank for rays id love to do something similar!