It appears that support for N-Wheeled vehicles exists, however I cannot find any documentation on how to create a vehicle which doesn’t have four wheels. The most I can find is an answers post stating that additional code is required: Multi-wheeled vehicles (more than 4 wheels) - World Creation - Unreal Engine Forums
A guide/tutorial on the vehicle system at a more abstract level than just four-wheeled vehicles and also explanations of how the system works would be greatly appreciated.
The vehicle implemented in Ue4 is actually the PhysX vehicle library implementation with a wrapper on top of it (check the source code)
I am not sure the library supports N-wheels. You should either create your own vehicle in blueprints /c++ starting from Pawn or wait for some community tutorials /samples