How did you deal with the length of the USB and display cables? I thought after 5m or so things would start falling apart. Are there active extenders and can they can handle 240+ Hz?

Yes, Monoprice sells a brand called "SlimRun" which actually convert the signal to fiber optic and can handle 100ft runs for USB, DisplayPort, and HDMI. They are pricey but they work.

I haven't tried 240Hz, but I have successfully run 7680x2160 wide screen at 120Hz (using HDMI), and 4k144Hz (using DisplayPort).

Not OP, but he website addresses this: https://lanparty.house/#cable-latency