So! She's drilled, painted (black on the back wall) and plumbed.
I had to resort to cheating with the plumbing: Teflon tape and Magic Lube were used in a few places. I've decided that slip fittings are the bomb, and I'll use those on all future plumbing projects. All of the slip fittings turned out perfect the first time around, but I had leak issues with the 3/4" barb fittings and the threaded fittings. It is a combo of 1/2" tubing, 3/4" tubing, PVC pipes, and 1/2" Loc Line. And, it works!
Thankfully I installed a gate valve. A lot of water continues to flow out of the overflow after the pump is shut off. I'm guessing around five gallons. I only have around 15 gallons in my sump. I don't want to have to deal with water from the return lines too (though I will attempt to accommodate it). I guess my next project is a new sump.
The return pump is an Eheim Compact 2000. It is dialed all the way up, and it appears to be sufficient.
I've picked up two MP10s for it. Those are going to have to go in the back wall, though. Had I foreseen that, the returns would be in different locations. Hubby insists that the system needs to be in the living room, and the only possible location for it is a wall that is 36" wide. The MP10s would overhang and be too easily knocked off. I may use a couple of little powerheads to fill in for the MP10s' new location.