The inline pump should be rated for at least 125psi or higher. You don't add the inline pump's output to your stock output pressure. Some people actually replace the stock pump with a pickup tube when running an inline pump. You can pick up a Bosch or Aeromotive inline pump out of a DRAG kit for about $100 or so. Your stock rails and lines will be fine at that pressure, but you can't go too much higher on the stock injectors. If you run extremely hight fuel pressures on stock injectors for an extended perios of time(FMU setup at higher boost levels), you run the risk of your injectors being stuck open, or just general injector failure. That's why ~8lbs of boost is the most I would run with a 12:1 FMU setup.