watched the movie when I was 10; read the book when I was 13.
both media for me are equally the same, in terms that I dont prefer one over the other. but since you're doing this for class, read the novel first. then, try to watch the movie to pick out some major themes. i believe the film was able to showcase what the novel was trying to impart.
for discussion points, the obvious themes would be political issues [ie. Civil war], social issues, gender issues [most specifically, a woman's role/life/struggles in that era]. then you can actually tie in all those to discuss how those issues affect love/marriage, etc. just some suggestions.
ps. "frankly my dear, i dont give a damn!" *sniff, sniff* that very last scene of Scarlett's silhoutte in the movie, waiting by the tree, made me cry.