The single electron universe model fails once you introduce other particles - a muon can decay into an electron and neutrinos. You can't represent that if there's only one electron going back and forth in time.

The laws of physics do not specify an absolute velocity, and the speed of light is a maximum that any observer can measure any object going, no matter how fast the observer is going relative to some reference point.

The important context here is that velocities do not compose by simple addition, but by a Lorentz transform. If I see two objects moving away from me in opposite directions at half the speed of light, those two objects will see each other moving away at less than the speed of light. This is where you also see phenomena such as time dilation, length contraction, etc... come from.