What were the important developments in motion pictures during the 1920's?

You seem to be in pretty good shape with the radio aspect of your project.  I would add that KDKA in Pittsburgh was the first radio station.  Also, research some radio personalities of the 1920's like Graham McNamee, who was a baseball broadcaster.  You also could discuss the impact that radio had on the popularity of sports.  That brings us to your topic of movies.

The decade of the 1920's saw a surge in attendance and profit for motion pictures.  The decade experienced a robust economy and more Americans had disposable income (why).  They also had more free time thanks to the workplace reforms that occurred before World War I.  Millions of Americans flocked to the movies.  They went to see the famous stars of the five major studies (who). These stars became trendsetters in the same way that they are today.  Some of the popular stars were Mary Pickford, Douglas Fairbanks, Charlie Chapman, and Rudolph Valentino.  In 1927 (when) the first talking picture, The Jazz Singer was released, which marked a new era in film history (What).  Al Jolson was the headliner for the film.  Over 80% of films in the 1920's were produced and shot in Hollywood (where).

You did not make reference to what type of project you were to complete.  If your teacher did not specify, you could create a web page on Weebly or create a timeline on Hstry.co.