Is this wiring safe?
Having more than one conductor under a screw is usually illegal and considered unwise. Pigtails would fix that. 
It's not uncommon to see a hot chained across multiple switches. ("Jumper" is a better term--"traveler" usually refers to three-way switch wiring.) The only concern there relates to question 1. Again, change it to a pigtail configuration.
We can only guess. You'd normally trace the downstream conductor, but there apparently isn't one.