This answers most of your questions:
Handling air-sensitive reagents | Aldrich Technical Bulletin AL-134 (https://www.thevespiary.org/rhodium/Rhodium/pdf/anhydroushandling.pdf)
(https://www.thevespiary.org/rhodium/Rhodium/pdf/anhydroushandling.pdf)
You seal all glassware joints with septa to keep oxygen and/or moisture out, and you introduce reagents with syringes, with which you pierce the septum and inject the liquid (adding solids under inert gas is a hassle, use a solution if possible). If you use an inert gas* then you let a very very slow stream of nitrogen or argon seep in* through a hose adapter and out through a needle stuck through the septum you have on the top of the condenser (or a side-arm of the flask). This "bleed capillary" is very important, or else the setup will fly apart if you let the gas pressure build up inside when adding reagents, if the rxn evolves gas and/or by the force of the inert gas stream.
A mag-stirrer is perfect for stirring under inert gas - there are gas-tight overhead stirrer adapters available but they cost as much as a cheap mag-stirrer... The inert gas is used until the reactants has been used up and/or until the reaction has been quenched, for example by adding water through a syringe.
* Optional in this case, the important thing is that you keep the air out, not much of the reagents will be destroyed by the small amount of air inside your apparatus, unless you live in the tropics.
* You need a very very slow stream, just enough to have a slight positive pressure inside, so that the outside air does not seep in, butonly the inert gas seeping out.