LOL...it's always after the fact, isn't it?
i really like external O/F boxes, but for SH, i'd recommend having a toothed O/F rather than a slotted one, which will be hard to do in a glass tank. if it were my project, i'd set it up similar to my 50 gal pent SH setup, but not quite the same.
i recommend a central trapezoidal O/F.
for your main returns, you can run two "over the tank" returns, or drill them and use 3/4" B/H's with wide flares.
run 2 or 3 CL returns about 6" from the tank floor on each end. of you run the 3rd CL return, put it in the bottom of the tank in front of the O/F box. i run strainers rather than flares on the outer CL returns to diffuse the flow, and a Y sticking up thru the bottom for the center return. the two outer CL returns are on a SCWD. i have the CL intake about halfway up one side of the tank. i used a threaded spa screen on this B/H.
if you like, you can use a SCWD on the main returns or not.
anyhoo, that's how i'd do it. oh, and i'd run with a black back as well, either ordered or DIY.
HTH