Ok..no need to respond in PM then. I would really want an overflow box over those holes. At least the 2 in the foreground. You see, if any one of those bulkheads leak, you will have to empty the entire tank to fix them. If they leak when you aren't home, you will come home to an empty tank. Can you find someone who works with acrylic, to make you a box you can cover them with? I suppose you can't do much with the lone hole, so you can use that for a return, or a closed loop, coming over the top with return.
this all depends on how much water you want going through the sump. If you don't need both holes in the foreground as drains, you can use one for drain, one for return, and the single hole as a closed loop.