IMPERSONATION OF AN AMERICAN TALK SHOW. HELP ASAP ;)?

For one thing, you need to decide what kind of talk show you want to do. Leno, Letterman, Ellen and Fallon are more comedic with celebrity guests, and the remainder are more "self-help" where the hosts help people solve their problems. If you went the comedic route, you could have roles for a host, a bandleader, and guests. Ellen is always inviting people from the audience up on stage with her, so there's some more roles there. A self-help show would probably be your best bet as there would be lots of roles available with a host, people with problems, and guests like doctors and other experts to help people with their problems. There should be clips of all the hosts on YouTube if you need help imitating their styles and their shows' formats.