I can easily imagine why someone could use 3 UR824’s: you need all those channles to record a live band.
Now … along with UR82M? If they use the same driver, I can understand. UR82M is your primary interface and monitor controller and UR824’s are for additional inputs. But my guess for why seeing all these equipment in single shot is: It’s Steinberg’s demonstration setup. All the stuff may not be used at the same time.
Probably not. What you’ll need is:
As many inputs as you think you need and few more for the cases you didn’t imagine would ever happen.
As many outputs as you think you need (monitors, headphone mixes, outboard gear sends, …) … and again … few more
Control devices (MIDI keyboards, drum/percussion triggers, transport/mixing interfaces) suited for your workflow.
Depending on what kind of “wiring” you mean, you’ll find answers from product manuals, audio engineering tutorials, computer manuals, etc …
Nobody learns this stuff fast. It’ll take years or decades to master your skills as an audio enginerr/sound technician.