I'm looking to build something similar. I see you didn't do a standard overflow and just used bulkheads. I like that. It seems much easier for me to do.
How is the sound and performance?
I have a lot of 90's in my piping, so I ultimately had to install reverse durso's in the sump, but it's virtually quiet now. Performance is good, I have a gate valve on one drain so that I can tune & not get gurgling sound. You have to drill the holes pretty close to the rim so that water level is high enuf tho. I had the guy that built my tank drill it for me. It's 3/8" glass. I used two 1" bulkheads as my plan was to have 2 returns running at a time for a total of 4, but ended up only going with two 1/2" returns (one running at a time & switching with a SCWD), so my drain with the gate valve is dialed back quite a bit (75-80%). If I had to do it over I'd use 3/4" bulkheads. My goal was not to have any powerheads in the display & I have plenty of random flow from a DCT8000 & the SCWD switching about every 6-7 seconds. So it's working just as I wanted.