What I find interesting is that the plane wings are modular enough to actually do stuff like this. Pretty cool!
Not really. The 5th pylon is an original design item and is only on the the left wing. When the 747 first started operating, IIRC there were no cargo aircraft big enough to transport fully assembled 747 engines so there was a real logistical concern about transporting spare and faulty engines to and from far flung destinations. It's kind of a relic of a certain age between the dawn of large turbofan engines but before the growth of the modern aviation industry.
The presence of that 5th pylon does mean some 747 get used for some interesting things. Virgin Orbit launches their rocket from a heavily upgraded 5th pylon.
No idea whether any twin engine jet has a 3rd pylon. My guess would be the asymmetry would be much more difficult to handle for offering regular passenger flights.