I'd propose the following setup.
3-neck roundbottom with stirrer in mantle as per your illustration.
Neck 1: Temperature probe through septum or thermometer through quickfit adaptor, ensuring it isn't in the path of the stirbar and doesn't touch the sides.
Neck 2 (central): Condenser with air outlet running to schlenk line.
Neck 3: Glass stopper, use for addition.
Assemble as above, except with glass stopper instead of thermometer. Evacuate/refill with N2 3x, Add reagents, repeat. Swap out stopper for thermometer, begin heating. If you do it this way, you will be under a blanket of N2 with no need to have a constant flow which would depress the internal temperature and make heating take longer. Just keep the schlenk line open with just enough N2 flow to be visible in your oil bubbler.