here's diagram fr rban on RC but the concept is rather simple, two holes. The Overflow chamber can be internal or external.
The diagram shows the main drain coming into the side of the sump but it doesn't have to be. Use a gate valve rather than a ball.
As for drilling the sump, assume your planning an external pump. Think how you're planning on placing the return pump and laying out the sump, that will give on idea where to drill. For the overflow chamber, if internal could just have a diaginal in the corner.
For the overflow, make it from glass and so you don't have to worry about the silicone not holding, can line with a thin sheet of dark acrylic.
If going 1" primary drain, can flow about 600gph, 1.5" close to 1200gph and that's a fair bit for a return on a 72g. Often for additional flow within the display, people do power heads or CL.