4). how does the stoichiometry of a reaction (balanced equation) affect reaction rate?

The stoichemistry is to do with the conservation of mass in a chemical reaction so that the mass of the reactants equals the mass of the products. The reaction rate will be affected in such a way that the reaction will proceed at such a rate as required to produce an equal  amount of product so that as the product amount approaches the reactant amount then the rate of the reaction should slow down.