Reviews on that rack suggest that the threaded holes are not very good, I’d plan on having a few rack nuts for rails that are drilled. Then if a hole is wrecked, drill it to about 1/4 inch and use a rack nut.
Mine I made a simple rectangle out of some steel tubing with rough welds on the corners. Everything else is 1/4-20 fasteners to hold it together. Generally you don’t need rear rails unless you are going to install some servers, and then you really need something deep. Front rails with a diagonal brace fromt top of rail to rear of rectangle worked fine.
This is the type of rail I used https://www.amazon.com/Reliable-Hardware-Company-RH-8-SRR-Space/dp/B00JQYUEA2/ref=asc_df_B00JQYUEA2
I’m also lucky enough that we have several shipping brace panels from much larger racks at work, made it easy to set the spacing between the rails.