I'd never drill anywhere near that many holes in a 45 breeder. You need one hole for your tank drain and one for the closed loop drain, although you could do that over the top as well if you wanted. There is no reason to drill return holes, just put them over the top. I'd also never drill a hole near the bottom of the tank unless it's protected by an overflow, that is, unless you're willing to take the chance that with any leak in your plumbing the tank will drain down to the hole, as Jeff said. I'd put the closed loop drain about 2-3" below the water surface in a corner, and your sump drain in the other corner. If you're planning on a corner overflow, you might as well put that hole in the bottom of the tank, if you're planning a calfo style, which is kind of what it looks like, they're in the right place to my eye.