Thevenin voltage (Voc) with a resistor in the way?
Your calculation of the Thevenin voltage is correct. R3 does not affect the result since no current is flowing in R3 and hence there is no voltage across it.  However, it will affect the Thevenin resistance so it will affect the voltage across a load connected to the red terminals. As for your second question, the Thevenin voltage is defined as the open circuit voltage at the load terminals so it will appear there in series with the Thevenin resistance.Voltages do not require closed circuits, currents do.