Some schematic questions

[CapnKernel]

I'm looking at the schematics here, and I have some questions:

  http://pypilot.org/schematics/hbridge_controller.pdf
  http://pypilot.org/schematics/tinypilot.pdf

• What is the purpose of R1 (100R) between +12V and the nano's VIN?  (Getting 5V from the nano is a clever trick)
  
  
• What is the purpose of U3 (BAS4002A)?  
  
  
• How is power fed to the RPi?  (I can't see it on this schematic - is it via the USB port, or perhaps via pin 2 or 4 (5V)?)
  
  
• If powered by 12V, the schematic says there should be a diode between J5 pins 2 and 3.  Does +12V need to be regulated, or is Vcc - Vf ok?  (For example, what if Pwr+ is 14.4V?)  And will the energy and/or voltage lost across the diode be worth worrying about?
   
  
• I'm guessing PWMCL is the clutch control.  Is PWMCL connected to anything?
  
  
• Is there currently support for a buzzer to signal errors, or that a waypoint has been reached?
  

Any pointers appreciated.